Questions from a newbie...

Well John, They can all be made to work

I'm a big fan of 360s, and a big fan of the A833.
As to the 4-spds, Yes the A-bodys and Fs use the shorttail tranny. The reason for this is to put the shifter mount in the correct place, so that you can actually mount the shifter. If you look in the tunnel, you will see a big old U-bracket spot welded to the underside of the tunnel at the rear mount. the shorttail puts the mounting pad in front of that. Then you get to cut out the side of the tunnel, to fit the shiftrods. Then you buy, and weld in, a floorhump, install a new carpet, dress it up,and you are in business.
That's the easy way. See below for "my way".
>As to the output shaft size;choose only the large one.
>As to the inputs; Originally only the hemis and 440-6bbls got the coarse splines, and the gearsets were also made to handle the brute torque that these engines put down on the racetrack. For the street, with street tires, IMO they would be pricey overkill.
>Clutch discs can be had for either sized input and for any size clutch.
>As to ratios;
There are three direct drive ratios and two overdrives.
The right ratio to choose Depends on the powerband of your engine, the rpm of peak power, and the application.
The overdrives,IMO, are only suitable for engines with low-rpm cams.By 220*@050, the splits are getting unreasonably big. You can drive these on the street, but they really drag the Rs down on every shift,So you will need some sharp tuning and lots of compression to be happy.And the low-ET for your power level will prove that they are a poor match at the track.
The direct drives have three applications. There is a close ratio for road racing, a deep low one originally designed for the 273 engine back in the early 60s, and another one for everybody else. If you have enough torque, the deep-low tranny will allow you to run two sizes less rear gear, so you can still cruise the hi-way. They are only good on the street with up to 3.91s. After that, first gear is getting crazy deep.They work really well with 3.23s to 3.73s, but your engine better have some oats to pull second gear.
If you want some help with gear selection, I am willing.

>My way
Go look at some factory floor-shift examples. Notice how far forward that shifter is. Getting into third in the heat of battle with long legs, has always been a challenge for me. I solved it with a longtail tranny.
The Longtails come with a shifter pad at the B-body location and with a dual position B/E pad. I used one with a rear pad. I drilled a small hole in the floor where I wanted to put that shifter, quite a bit further back. I have buckets. Then I poked my head under the car to see if that was doable, and I thought yes. The position I chose was with the seat comfortably located, such that I could push the clutch pedal down far enough for it to work, and of course still be able to steer the car. Then I hung my arm straight down. Where my palm fell, is where I cut the hole.Well I had to move it over to the passenger side so I could still find sheet metal to screw the boot to. I just cut a little starter hole, in case I had to move it a bit. Then I bolted the tranny in. The first thing I ran into was that I could not bolt up the rear mount. The interference point was that pesky front pad. I hacked just enough off to provide a rattle-free clearance, then bolted it in.
I had an old Mr.Gasket short stick "Bang!" shifter that I wanted to run. And I wanted to put it up really high, so I could put the top bolt in from the cabin side. So then I grabbed a piece of cardboard and mapped out a new adapter.Then I made it from 1/4 in steel flat stock.By now I was married to the longitudinal placement, si I cut the hole just big enough to drop the shifter down. Then I made some spacers to move the shifter laterally to where I wanted it, and trimmed the hole over to the passenger side.
>Of course while this was going on, I always kept in mind that the shift-rods, still had to connect the dots when I was done. So the position I finalized, provided an amazingly straight shot to the tranny.
I mounted the shifter on only the top bolt, not yet having finalized the angle I wanted to run it at. Now I did that. Checked below, that it was all good, marked it and finished it.
>Then I fabbed up the extra-long shiftrods.I use some 7/16 cold-rolled (I think that's what the provider called it) seamless tubing. I tapped the shifter end for some fine thread ready-rod. At the tranny end, I cut the ends off the Mr.G rods, and installed them into the levers. Then I bent up the rods the way they should go, inserted the tranny ends, hung the shifter ends with the shifter locked in neutral,and indexed them. Then I tacked those little guys in there, double checked the fitment, took them down and finished the job.
>Then I went for a roadtest. What a treat to have the shifter where it shoulda been all along. Back to the shop to do something about all the hot air and noise coming up through the floorhole.
>You cannot do this mod to the shorttail. The shifter pad is on the wrong side of the tunnel-brace/tranny mount.And you cannot do this mod with a bench seat.Well you could, but your upholsterer will have to get creative. I have seen that done.

>As to engine selection: All will fit and all will work.
Its a fair bit easier to stick a small block in there.
I'm a fan of the 360 cuz; Cuz it's versatile. You can build them for torque, for power, or for economy, or for a bit of everything. Any target compression ratio is easy to get. Heads are out there for any reasonable power level, and there are a Zillion cams to choose from. And they can rev!.If you have never heard a 360 screaming at 7200, for 8 seconds, you are in for a treat.
On the street they have more than enough power to be a lot of fun.
For a street/stripper 12s are easy, and cheap.
For a weekend warrior, they can be brutal.
For a long distance cruiser, they can be set up to pull 65=1300rpm
That's versatile.

BTW
During the years I was developing my combo, I learned to remove the tranny in 17 minutes,on a drive-on hoist.That's GVOD included.I didn't even break a sweat. I have witnesses,lol.
What's the point of that little tidbit?
When you go on vacation, an OD tranny can be less than 40 minutes to install.
A rear end swap is about 80 minutes.
OD trannys can be had at swap meets for $50. The bellhouse,IDK.I can't see getting a 2.76 for that.
The standard box and a 2.76rear will get you roadgears of;
7.64(seriously dog)-5.27(pretty lazy)-3.84(who cares)-2.76 (awesome cruiser).
The overdrive box and 3.73s will get you roadgears of;
11.53(lightning)-6.23( still snappy)-3.73(who cares)-2.72(awesome cruiser).
Y'all come back now