I use a YS 110 on mine. It's a great engine. But you better be careful, really careful not to overspeed this airframe. It will fly apart in a heartbeat if you over speed it. My guess is the 120 would be a great engine also.
This is a favorite plane of mine. I love the UCD. I've had the 46, 60 and Giant. The 60 is best for me. It's one of the funnest airplanes you'll ever fly. Lands so easy you'll think it's a trainer, yet when you turn it loose it'll 3D with the best of them. One of the few planes in the world that will do a rising flatspin, my favorite maneuver. It's easy to hover, does a great rolling circle, wonderful flat spins, and the waterfalls are outstanding. It's weakest point is Harrier and KE. But, keep it away from that and it's great fun.
Put your 120 on it and go out and have a ball.
Thanks
BArry