driveshaft length same for coupe/fastback?

Should be exactly the same.

I think the length should be the same for a coupe and a fastback, I purchased an alum. driveshaft for my '66 Fastback thru Mustangsplus. It had it for a few months until I was ready to install it, and then I found that it was too long. I called them and they sent me the correct length and credited my card back when I returned the wrong one that the originally sent. They were real helpful, and didn't have any problems w/ me taking a few months to discover the problem.

If it's too long or short you can also sometimes swap the yoke on the rearend to compensate. Ther are at least 2 different length yokes for 9" rears, probably the same for the 8"