you have to mod the tunnel for the clutch fork and the rotor gearboxs are a bit fatter so the middle of the tunnel needs to be made taller, the gearbox cross member is piss ant easiest thing to do you could probably use a maddat ca18 crossmember. for the motor because the eccentric shaft is up higher in the motor (compared to a piston engine) it has to sit fairly low, most people use the front mount system so with the a12 crossmember you just chop the a12 mounts off and you have to cut out the crossmember where the 12a sump sits (and re-brace it) so you get your 15mm clearance or what ever it is. for the front mount you just buy an rx3 setup and mod that or make something similar. also you can do the shifter extension mod so the shifter doesn't sit so far back in the cab

there's a bit to it but if your handy with the tools should be no drama, as for it being legal nowadays wouldnt have a clue