Drive shaft yoke slip play question

[bikemikey]

I'm working on my 81 Chevy swb Silverado. I changed out the old 350, ( it came with a 305 ) and changed out the old Turbo 350 with a 700R4. I had trouble installing the drive shaft so I figured it was too long. So I took it to a drive shaft shop with the measurements and he told me it was too short. Come to find out the slip yoke was bad, but he said it would probably work , so we replaced it. Now I'm thinking he was right in the beginning and the shaft is a little bit short. Here are the measurements. The slip yoke is 4"  long of which 2 1/4" sticks inside the trans tail housing,  that leaves 1 3/4 inches of yoke exposure. The tail shaft sticks out 9/16" past the seal of the tail shaft. If you add 2 1/4" plus 9/16" that gives you 2 13/16" of driveshaft spline engagement. If you subtract 9/16"  from 1 3/4"  that gives you 1 3/16" of slip yoke play, or lets just say 1 1/4" to be safe. My question is, does this sound safe, I know 1' or 3/4" would be better. The truck is sitting on the ground with no weight in it. Appreciate any opinions.

Thanks,

Mike