Which glow engine for Firebat?
If these are small stick built electrics, the conversion to glow from electric has a few more pitfalls than the other way around. Generally electrics are built far lighter without the need to deal with the vibration of a glow power. I would be carefull about beefing up the engine area as well as the wing dihedral joint area. Another area to watch on stick builts is the leading and trailing edge of the stabilizer.
If they are foamy electrics then be carefull of a powerplant that is to large, small foamy unreinforced wings can be quite flexable and lead to problems if overpowered.
John