Basically the ls1 nets more power now. Finding one takes some searching, but you'd have to mod a lt1 to get to ls1's stock power. Making the 2 about the same in price (depending what was paid).

For the tranny's.. you can use the newer t-56's on an lt1, that hole just stays a hole.

Check out hpsalvage.. i think their site is www.hpsalvage.com and see what he says.