Jap Performance Parts put an RB26 in their GC8.
Saw it in a recent issue of some magazine, thought it was import tuner. It required a ton of work including cutting the tranny tunnel and firewall to get it to fit. I think you'll love the SR. You can make more than enough power there for this chassis in my opinion.
In terms of engine/ trans dry weight, EJ longblock w/ acc ~ 250lbs , 5-speed ~ 150 and 6-speed ~ 225 I think.
SR with tranny is ~475.