Please note that I posted this from information in other threads, and modified it when I gathered new info so it might not 'read' that well.
Driveshaft info:
When swapped into a car that came with a 6.75” rear, the 8" rear pushes the stock pinto driveshaft forward about 1" or so; I would assume that Ford put a shorter shaft on them. I have never had any issues with 8" rears and stock driveshafts for the 6.75" rear, but the t-5 is longer than the stock pinto trannys (auto).
Pintos have different length driveshafts for different trannys and rears. I had a set of wagon leafs and the pins were the same distance from the front mounts, so I know they have the same wheelbase.
A driveshaft from a stock fox body will fit a T-5 to 8” rear IF the engine and tranny are in the STOCK LOCATION. Be aware that when I searched I found that the Fox body car can have up to 7 different shafts, depending. Be sure you have the correct length, year and yoke.
I found the 77 Pinto m/t has a shaft about 43" weld to weld, and the a/t ones are about 44". Add 2" on either side to get on-center of the u-joints. The 8" rear pushes the shaft forward about 7/8" and the t-5 is about 1.75" longer than the stock c3. A shaft about 41" to 41.5" weld to weld (45"-45.5" at the u-joints) should be fine. Of all the ones I listed above, the V8 m/t one is the shortest at about 41.5" at the welds, but has the bigger u-joints DEPENDING on what year; the 86 and older ones take the same, front and rear as the Pinto FRONT. The Pinto rear takes a u-joint with two different size caps.
I still had the driveshaft from my 79 2.3 4spd racecar. I put the a/t and the m/t shafts for 6.75" rear Pintos side by side. The a/t one is just about 1" longer. The 8" rear pushes it forward a little less than that, but I used the m/t one in the orange a/t car (last night) when I installed the 8" rear.
The following information is based on the 77/78/79 parts I have, or the swaps I have DONE:
C3 - 6.75" 48" on-center of u-joints
4spd - 6.75" 47" on-center of u-joints
C3 - 8" 47" on-center of u-joints
C4 - 8" OR T-5 - 8" 45.5" on-center of u-joints
I never did one myself, but with the information I have I would assume that for a 4spd - 8" a 46"-46.5" (on-center of u-joints) would be needed.
The C4 trannys are longer than the C3's and the 4spds. I had a driveshaft shaft that was marked "2.0 Pinto" that was 45.5" O/C. If that was correct, it was most likely from a C4 - 8".
The end caps on the Pinto unit that u-bolt to the rear have a BIGGER diameter than the ones that are in the yoke, that is why they are different, where the fox ones are both the same size (but different sizes depending what year).
I installed the Pinto rear u-joint on the early fox driveshaft with no problems.
BTW: The EARLY fox u-joint will 'bolt' to the Pinto pinion, BUT the u-bolts will not clamp the u-joint properly to the rear axle. It will pinch, and over time (or abuse) cause it to fail. 2 of the 4 Pinto rear caps are 1.125" X 3.218" (overall width) that bolt to the rear yoke. IIRC, the other two are the same as the 4 on the front joint: 1.063” X 3.218”. The later Fox body ones are like 3.5" wide.
An AreoStar rear driveshaft from a 94-97 WITH AWD is also 45.5” O/C and Ford made some of them in ALUMINUM. It has the same u-joints as the early Fox (pre 87) and Pinto fronts, 1.063" X 3.218" wide, both sides front and rear. I have one of these in my yellow car and I will be putting one in the orange car when I do the C4 swap.
The yoke for a C3 will fit the PINTO 4spd. The slip yoke for a C4 and a T-5 are the same.
Also, after some measuring I did notice that yokes can be different lengths, from about 3.5" to 5", even if they fit the same trannys.
NAPA part #372 u-joint has the correct caps and width to install on the later Fox driveshafts and still connect to the 8". IIRC: You might have to swap the Pinto caps to it but they do fit (I did a BUNCH of measuring).
The only thing I have needed to do is swap the caps on the u-joint and use the same driveshaft.
I would like to state this fact again: The 8" rear yoke (where the u-joint bolts) is made for a cap that is 1.25". The fox body with the u-joints that are 3.218" wide have cap diameters of 1.063" on all the caps. The Pinto and 60's Mustang joints (maybe others too) have two caps at 1.063 and two that are 1.25". A 1.063" cap will bolt in, but is not correct
The 1980 Pintos call for a different part # rear joint, but I don't know why.
Bill