O.d.

I dunno about your best option as it pertains to a manual.
But I am sure the 833 O/D is not it.
But heres something to think about. It sounds to me like your biggest concerns are to keep the revs down at 75mph, and you really want a manual tranny. If this is right, and you had a small block,then you would really need a 5 speed, to get back some off-the-line, giddy-up. But with a lot of cubes, comes a lot of torque, so getting off the line is less of an issue. Depending on your horsepower level desired, versus reality, there is/are other options.
If you are willing to go easy on the cam, I can offer this suggestion, which is what I have settled on; The 3.09 low/Direct 4th box with a GV behind it, and 3.55s.I will use Bold numbers to indicate GV ratios.
The ratios are 3.09-1.92-1.40-1.00-.78,
With 28 inch tires. this will work out to about 2500rpm at 75mph.
The starter gear will be 3.09x3.55 =10.97 which with the standard box is about equivalent to; 10.97/2.66 = 4.12s, not too shabby.
The splits are 62%,73%,71% and 78% into od.This means outshifting at say 6300, the rpms will drop to; 3960into 2nd, 4663into third,and 4535into fourth.The big engine will have no trouble pulling outta these drops. The powerband requirement will thus be about 6300 less about 4600 =1700 rpm. You won't need a whole lotta cam for this.
So let's look at this;
Big engine = big torque, so don't need big gears to get off the line; so that 10.97 starter will be more than, ok,
and tight powerband means small cam is ok. Tranny splits are excellent,
starter gear is excellent,
overdrive gear is excellent.
You might be looking at the 1-2 split. The drop is to 3960, and it happens at 48 mph. Fair enough that's a bit of a stretch.So I'll tell you a secret; The GV will take full power, and can be used as a splitter. If you split the 1-2, the ratios are 3.09-2.41-1.92-1.40-1.0-.78. See anything you like there? Heckyeah 6 gears!
Ok, now, the rpm drop into 1od is .78, so from 6300 will drop in at 4914 Whoa!. And 1od into 2nd will be .80, so from 6300 will drop in at 5019Sweet! So now you have the powerband down to 1500 and change.
Now if you wanna track this car expect to crank out about 115 or better, then you will need a final drive of 4.70 to perhaps 4.30s. Well, 3rd is 3.55x 1.4 = 4.97 so that's a little steep. But 3.23s and 3rd is 3.23x 1.4 =4.52 Right smack in the middle. So, back up the bus. Since we have Gear-splitting capability, why not pitch the 3.55s and just compromise with the 3.23s? What? you ask who tracks with 3.23s?
Well check it out; Why not split 1-2, and 2-3? This makes just one pull on the stick and 2 electric lightning GV shifts. Interested?
The ratios are 3.09-2.41-1.92-1.49. and the rear is a 3.23.The starter gear is 9.98(equivalent to a regular box with 3.75s). The trap gear is 1.49x3.23=4.81(a bit out there). The hiway gear is 3.23 x .78 =2.52, making 75=2267rpm.
So what have you got? Well it won't 60ft like lightning. and that 4.81 FD will make 115mph at 6639rpm. But hey you could use third. Which is 1.4x 3.23=4.52, dropping that 115 to 6240! leaving you a lot of headroom! 6500 would get you 120mph.

There are two tricks to making this work; 1) a willingness to compromise your 60ft, and 2) a willingness not to shoot for the moon as regards a camshaft.These are real options for a streeter.
I have posted the gear ratios, so that you can play the numbers for yourself, and decide if it's for you. The splits are so tight, you will put a lot of average horsepower down.Keep in mind that there are 5speed options out there right now for a pretty good price.

I have been running the above combo with 3.55s and a 367 cuber in a 3650# raceweight 68Barracuda, set up for street, for over 12 years now. In 2004,she went 93 in the 1/8, the one and only successful run it ever made.I have no idea what that translates to in qt trap, but to me it was damfast.
I feel that two splits and tight ratios,in my combo are worth at least one or two cam sizes. My car is faster with this combo and a 230*(276 advertised) cam than it was with the 292/508 (maybe 248@050)and a regular 4speed.That's at least 3 cam sizes. And the 230* is sooooo much sweeter on the street.
I know my combo is just a little367, but it seems to act big.With the legal speed limit here being 62(100kph), and my 27 inch tires, cruising is 2137 with 3.55s.