Hey, John. I just had a drive shaft made for my 69 SS 396 four speed Camaro this last summer. From what I have found drive shaft length can differ from each car even if they have the same option. I had ordered a drive shaft from a known Camaro catalog and thought was all fine until I installed it and I ended up with a nasty vibration. So, what I did was go to the drive shaft suppliers website
www.dennydriveshafts.com. He had a printable form that you could fill in the blanks. I took the measurement and brought them to a local drive shaft shop and they made me one in about and hour. I'm not sure if they have one in your area but I went to a CATCO. I'm very pleased with the end results. I hope that I have helped you out.
Jesse