I think it will work just fine. It will be close to or just a few ounces heavier than the OS 1.20 4-stroke shown on the kit plans.

I've seen one of these kits with a Zenoah G-26. I've also seen several other warbirds with this sort of large, round cowl using small gas engines such as Zenohas, MLD's, etc. I have this P-47 kit still half completed and I can tell you that you'll have room for the engine.

It may balance OK or you may have to get creative with your servo and battery placement to hit the right CG. Try not to add weight if it can be avoided.

Actually, this really isn't a beginner airplane or setup by any means and you might get a lot better answers over in the warbird forum. I'll bet several of those guys have done something like this already.