It is my opinion that the 61 Four Stroke is pretty equal to a 46 two stroke.

My brother had a TT 46 Pro on an Ultra Stick 40. He was not satisfied with its performance. After looking at comments on RCU we convinced ourselves that a 61 Four Stroke would be an improvement. It definitely was not, and the 61 was replaced with a 70.

I know a trainer is different than an Ultra Stick but I would be concerned that a 60 size trainer is a bit too much for the little four stroke.