Os has come out with their AX series of engines: the 55 AX, 75 AX and the 120 AX. The 55 AX is the same footprint as the 46 and 50 are/were. You might want to take a look at that engine.

I have the 75 and three 1.20's and love them. They are 100% reliable and have plenty of power. Moreso than most of their counterparts.

CGr