It’s been a lot of years since I bought my Ford Motorsport Aluminum Driveshaft for $149 (before it was called Ford Racing), but I went to a Tremec 5-speed and had the issue with it being 1” or so too short. There used to be machined spacers with longer bolts available to fix the issue and I’ve been running that for many years without problems with 514 rwhp. Multiple companies made the spacers, but I don’t know if they still do. Try Tremec, Steeda, or LMR.
My last one cost $735. It's chromoly steel with 1350 u-joints and I purchased a Sonnax slip yoke for $172 from Summit. My story on why I now own three driveshafts is too long to write. It was a lesson well learned but very expensive. My last one was the most expensive but well worth it. The 3.5" chromoly seamless tube was so perfect it didn't need any weights to balance it. It just clears everything in the tunnel. I had the other two balanced as well. I have a T56 Magnum and a Moser 9" rear end so I had to get a new driveshaft because of the power my little 4.6 makes. Craftsmanship means everything when building nice parts. Here's a picture of the weld this builder makes and one from the builder before with the 3" seamless tube. There's the difference. They were both mig welded by hand. Get a picture of their work if you can or look when you go if you go in person. MAKE SURE IT'S BALANCED!
One more very important part of getting the right driveshaft is the length of it. It should have 1"-1.5" of space between the slip yoke and transmission flange at ride height. Any less and you could brake something. Any more and you'll have a vibration issue. If it's not properly balanced you'll have a vibration issue. Good luck with your project.
