I would not try to sell it incomplete. People will expect an "unfinished price".

Maybe you could offer it "as is", and if they don't like the odd motor combination, offer it for about $3,000 less, with no motor & trans. That way, they can drive it, and then buy it however they choose.

(I would not be surprised that some might think about the trouble of the swap, and want to use it immediately, so they end up buying it with the motor, anyway.)