They just take your ends off of the existing tube, put in a longer tube and reweld and balance. Not a big deal. Take it to any truck shop that makes driveshafts. Now unless you have 1000 hp, I would get someone else to make it.
None of those places have the ability to balance at the speeds needed for a race/performance app.
Been there, done that. Was like riding a paint shaker. One race old. It came out and went in the scrap pile. But not before beating up the good yoke and tailshaft.
Few years ago had one done for a customer car. Pretty mild combo. Visible runout.
Driveshafts are no joke.Use a shop that does race shafts. Send them the yoke, if it's a good piece, give them a C-C and pay them. Sleep better.
When I installed the S-60 in my Dart I had a driveshaft built by a very highly recommended shop in Michigan. After the install the car had a vibration, I played with pinion angles, rebalanced tires, rechecked the driveline angles, nothing helped. Finally, I had the transmission out for a converter change and called my local driveshaft shop to have the balance checked. It was waaaaaaaaaay out! He rebalanced it and it's smooth as silk even at 135 mph.
BTW, the shop in Michigan charged almost $500 for a "race" driveshaft, snake oil.
