[john hall]

I looked for a while for an 18hp Magnum and never found one cheap. Closest I came was a Craftsman mower that was ready to cut grass for $400--too much $$ given the condition of the mower I wanted it for. Larger Horizontal crank engines in general are had to find these days, most stuff is vertical. Got any pulling clubs near you? Some of those guys like newer styled machines and chunk all the running works so you may find an engine with that crowd.
FWIW, I think you did well on the purchase price. Keep an eye on CL, you may come across another entire 6 or 782 reasonably.