Just for a simple guide for these old timers, the SAM rulebook limits glow engine size to a 0.10 cu. in for each 225 sq. in. of wing area for competition. Most of the Bombshells I flew against used older baffled 40s, since if I recall, they had about 920 or 940 sq. in. wings. Something like an 11-4 or 11-5 prop with a 40 seemed to give a climb similar to what they got when using some of the older 60 ignition engines, which usually turned 13-6 or 14-4 props at under 10,000 rpm.
If you want to use larger engines, pay attention to the wing construction. Since in the thirties and forties, these planes flew under power till the small amount of fuel was burned off, and dethermalizers hadn't been invented, and the only RC devices were what a few hardy and courageous fanatics designed and built themselves, they were frequently lost out of sight, and so weren't really built too strong to keep the cost down. I think the Bombshell may have been at the upper end of the structural strength, though.