IMO, Ls1 or 6.0 is the way to go. They are easier to work on and get power out of.
We have 1 of 2 projects started along the same lines. We almost have the motor together to put in an '81, and after that, plan on doing the 6.0 in a '92 rcss.
Its a little more for the GENIII motors, but worth it to me.