It has 3.31s and it is a cruiser.

 

I have a 3.5 Denny's driveshaft with 1350 yokes on both ends in my 70. I'm running 3.70 gears in a nine inch and have no issues. My car is a street car but I do beat on it any chance I get.

 

I measured the tube length of my driveshaft and it’s 50.5”. It’s 3.5” OD and I’m not sure on thickness. But I should be good with turning 7k rpm in 4th (1:1)

 

Hopefully you don't have driveline vibrations. A-bodies are notorious for that when the rear ride height is lowered. Poorly engineered swap engine mounts make it even worse because they don't place the engine in the front crossmember as low as possible. I eventually had to go with a CV driveshaft from The Driveshaft Shop.

Andrew