I don't think the 350 would have any dire affects on your tranny or rear end. I use to run a 350 in my 64 Impala with the powerglide and theres a world of other old Chevies running that combo. He's probably gonna offer to take the truck off your hands for cheap and then throw a 350 in it and enjoy it himself. If you have any mechanical skills, swapping in a 350 ain't a big deal and you could do it your self for a lot less. Good luck with it.
