actually, i can talk from experience, i have droped an rb 20 det in the front of my prince gt, you can get the package with the gearbox of there is an adaptor to bolt the orginal L block gearbox to them. as for the tailshaft both the rb and L series gearboxes actually have the same yoke size and spline........ only thing you might have to do is fabricate a set of engine mounts.... the gear box mount is almosrt the same.. for both bolt positions on both gearboxes......
and i think there are mobs out there that have engine mount kits for these conversions... just need to look around abit..... zoom was a good magazine for these sort of articles and information.....
any thing is possible...and an RB20det would be a absolute V8 killa in that toy!