There are ways to do it. Look up 66e for various writeups. The two biggest problems are mounting the engine in a SJ hull and the exhaust manifold. WDK makes/made 66e upright mounts and Brandon Reed will modify your cases to fit in a SJ hull and fit SJ electrics. The exhaust from a GP800 won't fit in a SJ so a custom manifold has to be made to accomodate it or a custom exhaust system has to be made. I believe WDK is only one who makes/made a custom exhaust. Before you think about buying anything from WDK though, you might want to do a search on that as well since he is notorious for delivering late or not delivering at all and keeping your money.