Hi, BOB
the O.S. .61 might like another prop better. You didn't give us an rpm number, but I could pull an 8 lb pattern plane straight up with a 12-10. If you only have "a little bit of throttle left" you should try a few different props. Also, the bolt pattern on the firewall and motor mount will let you mount a motor sideways. The 3-D ace in our club uses an O.S. .91 4c with a 13-6 prop on his UCD .46. He hovers, tail touches and has a ball.

FRED