If it comes out of an R50, I wouldn't think there would be much issue with mounting the motor. It should have the same mounts as a VG. The tranny might be a trick. Do you know exactly which model it is? Is it full-time AWD or select 4WD? I don't think all wheel drive would be too practical in this situation. Then, if it doesn't match the WD21's transmissions, you'll have to worry about drive lines... Custom-built may be necessary. You'd be much better off if this motor would bolt-up to your existing gearbox. Of course, even if the drive train swaps over, you still have to work out the wiring (an included engine harness probably won't be directly compatible with the chassis) and difference in fuel systems. Having the donor vehicle on hand would help, All-in-all, it sounds like a nightmare. A time-consuming, cash-guzzling, ulcer-inducing nightmare. It ought to be a blast! Do yourself a favor and find the FSM for the R50 or E50 that the motor comes from and start comparing it to the WD21.