64 Barracuda 7 1/4 to 8 3/4 Swap.

TimS said
Sounds pretty doable. Don’t want to cut the original drive shaft so need to find one of those as well. Car has a 340 and 4 speed in it right now.

What trans? Still have the ball and trunnion front u-joint? If so, easiest thing would be just to shorten the driveshaft. Any competent driveshaft shop could do that for you. I'm not aware of any driveshaft with a ball and trunnion front u-joint that would bolt without modification into your 64 Barracuda with an 8 3/4 rear.

I have a later trans (with my original 65 gearset) and a conventional front u-joint in my 65 Barracuda. Driveshaft from a manual transmission 71 Duster 340 was exactly the right length for an 8 3/4 rear. (The extra length in the wheelbase of the 67-72 Plymouth a bodies is all from the trans crossmember forward.) So if you have a later 4-speed trans, a manual trans 71 Duster 340 driveshaft would work for you, too. (Because the Duster was a 3-speed manual, I had to change the front yoke, but the shaft itself fit without modification.) But I did all that a long time ago. Try to find a Duster 340 driveshaft today. Any 67-72 Valiant (not Scamp), Duster, or A body Barracuda shaft from a 4-speed car with 8 3/4 rear would also work with a conventional front u-joint, but good luck finding any of them, either. Again, shortening the shaft you have might be your best bet. Or, it's not that big a deal to have one made for you, either.