Like everyone else is saying, there's not really a reason to put a B18C5 in a G2 GSR. 5 grand for 35 hp out of a used motor is a bit steep.

But if you for some reason want to, keep your cable tranny. The gear ratios are identical so with a bit more work you can just put your cable tranny on the R motor and toss everything back in no problem.

What I would suggest rather than getting the R motor is a rebuild with high-comp pistons, new rods, lumpy cams, i/h/e, better intake manifold, etc.