Drive shaft length specs

I like what fishy68 said, and his info. I have a D.S. from a 727/8.75 combo that I drove for years, and I have another combo from a 904/7.25 that ran really smooth. So I should forget the yoke, and measure the shaft lengths. I will say though the 904/7.25 combo is much smaller in diameter, and tapered. So the one shaft is beefy, while the other has a taper, which theoretically should make it strong too.
I hate theoretics...