It's recommended 120 was a (1990) YS 120. I cannot say how strong the YS 120 was back then, but it sure seems like it would almost have to be less of a motor than today.

I've read about Saito 100s hovering (barely) 10 pound planes. I would not call that engine an "Unlimited" choice, but a good one for the Goldberg Ultimate.

I've flown the Goldberg Ultimate on an OS 91FX and felt it was "OK", but for my taste, not enough. It would not pull straight out of a hover, but did everything else.

What I've read says the Saito 100 is easily a match for the 91FX and may be a bit stronger on the 15+ inch props.

That is the basis for my prior statement.