Garfield, I flew my Decathlon 40 with a Magnum 52 4 stroke, turning a 12X6 prop. It was good power, but I found myself at full throttle most of the time, and I don't care for that circumstance. I switched to an SK 50 (2 stroke), same prop, but more power. Your ASP 65 4 stroke is probably a great match up for this plane. Go for it.

edit: typo, Decathlon 40