Unless I misunderstood things with new IVA regs what I'm about to write is total cock...But using anything other than the engine/box from the donor car won't get you an IVA pass unless you can prove it was actually fitted and registered with dvla prior to you stripping the car.

The only way non donor motors will pass IVA is as a low volume car and that means using bike motors too.

But like I said I might have got it all arris about face...