WOW!!! When you guys git on a role, you git on a ROLE. All this info is great. I appreciate it. But .......... somebody is gonna have to put all this in a nut shell and tell me which way is the best and most economical for a driver street car.
The conversion mounts will cost you $150. If you can find a v8 k-member for less go that route, they are easy enough to swap out. Irregardless of what has been said about weight transfer if the car is primarily a street car (even if you go to the strip occasionally) go with bigger than \6 bars. The .890" bars don't ride rough and make a dramatic difference in the handling of the car that you will enjoy every time you drive the car..
Definitely get disk brakes on the car. The 9" \6 drum brakes are woefully inadequate. Again if you can find a doner car in the junk yard the 73 and up factory system will be the most economical way to go. However, it might be cheaper to buy an after market kit compared to buy 73 and up parts off e-bay. Also, remember the 73+ stuff is going to have the bigger 4.5" bolt pattern so you will need new wheels but there are endless choices in the 4.5" size.
Again if you are going street car you want a 727 much more durable at the slight expense of robbing a little power. However, the 727 will also require that you shorten the drive shaft and get a new slip yoke to fit the bigger output shaft (unless you find a doner with a 727 that you can get the drive shaft from). Again it's a matter of economics. A 904 will be easier to come by but to beef it up will cost money. A 727 will be strong enough stock.
My 68 Barracuda was a \6 three speed manual car. My plan was always to do a v8 swap but I also new if the car sat to long that I would like never finish it so I made a plan and stuck to it. I recomend that you do that to. Here is my plan;
1. Do the paint & body work and redo the interior so I could drive the car as soon as possible. The rest of the activities I planned for winter when I was not going to be driving he car.
2. Start collecting parts for disk brake, rear end, cooling, 4spd and V8 swap.
3. The first thing I came across was the 4sp. I used an A833OD unit from an 81 pickup. This was actually swapped in when I was reassembling the car after paint.
4. I had an opportunity to pick up a 73 v8 Dart that donated disk brakes and the v8 k-member.
5. I also picked up an 8.25 rear end at about the same time. I rebuilt the rear end with 3.5 gears and sure-grip.
7. I also picked up a set of big bolt pattern rally wheels and refinished them.
6. I swapped to disk brakes (and installed the .890 t-bars at the same time). I also swapped in the 8.25. I had the tires that were on the sbp wheels swapped to the rally wheels. I now had a \6 4spd car with disk brakes and an 8.25 rear end.
7. I found a rebuildable 360 core for short change and rebuilt that motor over the winter. I had also picked up a radiator, v8 bell housing, flywheel, clutch and headers. The \6 had 6 into two headers and when I had an exhaust bent up for it I went duals and had it configured so all I had to do was cut the pipes at the end of the tranny to adapt them to the v8.
8. I then swapped in the v8 using the v8 k-member from the Dart doner.
After the paint and body work I did the all the rest over a 5 year period but never had the car of the road for more than a day or two during the prime cruising season of April through November. I have put 30k miles on it with the \6 and another 20k miles with the v8. Every winter I plane for another upgrade. This past winter I swapped on 15" wheels, the winter before I did manual to power steering and the winter before that I swapped in another exhaust that is nore appropriate for the power the 360 makes. I am now collecting parts for AC.