The idea of buying a running vehicle with a 350 engine sounds like a good one,course you could always buy a GM crate engine,but that would be quite costly.Probably a couple grand.I have a 700R4 in my 55 2nd series and really like it.I am still running the 3:90 stock rear.A small Chevy Blazer rear should fit right in,but measure it first.3:73 gearing should work real nice with the 700R4 I am planning on switching rearends in mine in the near future.