Luke, Just pick up an 18RG, and put a Corona sump and oil pickup onto the bottom of the engine, bolt up a W5- gearbox, and drop it in. Small adjustment to gearbox X member. ( from memory, I think auto one does the job) Tailshaft simply needs the spline end changed over to RA spec. Upgrade the front brakes by putting in a complete RA23/28 strut. 2 Litres Twin Carbs, lots of induction noise and some tyre frying action await. Most of the other engine conversions require lotsa dollars, and will take heaps of time to do properly.