driveline play

[78chevstepside]

I recently lowered my 78 stepside 4/6 with a notched frame and new spindles shocks and coils. My truck origionally came stock with a 250 6 cylinder and three on the tree tranny. Curently iam running a 355 with a turbo 350 automatic. I am still running the stock three speed driveline. When i recently noticed my rear seal in my drivline is leaking . My driveline is too tight. Everytime i hit a bump i bet its pushing my driveline into the tranny. Does anyone know how much play there should be in the driveline? Couldnt a person just cut the yoke to gain a inch of play? Anyone had to shorten there driveline after dropping the truck? jay