While I value Opjose' opinions, I have to disagree with him on his engine choice. Spend the extra $12 and go with the Super Tigre 34-----MUCH more reliable engine with very tall thin cylinder head cooling fins that work very well on a pusher engine configuration. I've got a 40 sized Long-EZ that I swapped out an OS 46AX for a Super Tigre GS45 and the difference was night and day.
I'm also running one of the 34's on a Bridi Sun Fli 4-20 and a pair of the 34's on a twin.

I've had ONE GMS engine, it was a 75 or 76, and upon the initial running of the engine for breaking in it abrubtly stopped. I turned it over by hand and it had NO compression. Took the head off and found the piston ring sitting on TOP of the piston! Sent it back for a replacement and wound up trading it off.

Rube