gabarber:

I had a 40 trainer with a 60 engine that did not live long.

More weight at front = more weight at the tail = heavier model = faster flight and landing / more inertia during maneuvers / harder crashes / higher fuel consumption.

What for? A little more of speed?

Trainers are designed for having high drag and strong decalage, which do not match with high speeds.

I am repairing the thing to be propelled by a 40 again.

More power is good for 3-D or for higher speed; I believe it is better used on a suitable model.

Regards!