Truck tranny in Z?

Have been wanting to put a 5-speed in my '76 and just realized the other day — D'Oh! — that I have an old 5-speed left over from my Datsun truck days. It's a 5-speed out of a 77 or 78 620 truck. Now, according to the one truck manual I still have, both trannies are the same model, but the truck transmission is geared slightly lower in first three gears, fourth is 1:00 for both, and fifth is again slightly lower for the truck. Has anyone used these trannies in Z cars? I couldn't find much about it in the archives. If it would fit, wouldn't the lower gearing make changing to a 3:90 rear unecessary?