If you are talking RV8 into sierras done it on a xr4i.
3950cc crossbolt block,(TVR) soon to be fuel injected as well running EMERALD ECM.
EASY to do, manifolds can be a pain, took 1 1/2hours to get roughly into place with gearbox and engine, uses R380 gearbox.
Problems included twisting and snapping the prop clean in two one day, smashing rad(rover one) on hump as it is a lot taller, PACET FANS continually packing up, KENLOWE ok though.
If you want any help just PM and I'll give you my email addy.
tabetha