The 40 FP (while a great engine) will be pretty anemic for the 60 size trainer. If flying off a grass strip, it is entirely likely that it won't get off the ground. Today, a standard 40 like the FP, is considered too small for even a 40 size trainer by many, but is what I learned with and it worked fine. A standard 60 size engine would work much better.

Selling one of your bikes might provide your first months hobby income, but what will you do for the next couple of dozen years? [X(]

Welcome to RCU and the best hobby in the world!
Dennis-