HI Bill & Gene
In case that is it, I would use the muffler on break ins with all of those engines, I don't think you would overheat any of them using mufflers, As alway the caution I gave when doing this is NOT to get the motors into a lean 2 cycle, be careful to run them in richer.
I have never had any problems breaking engines in with mufflers on them, in fact engines need to be at temperature so they can break in heat cycling at where they will operate.
I would also say use a lightly loaded prop when you do break ins
Example you may run a 12 x 6 on a ST G51 I use a 12 x 3 or 12 x 4 prop for breaking, I use a 10x4 or 11 x 3 on a FOX 35 for breaking. Magnum 36 I also use a 10x4
Regards
Randy