Assuming that you're not going to enter a contest, any 29-to-40 will do just fine.  A modern 25 would be better yet - lighter and generally more powerful than old 35's.  These old planes were small.  You will be happier with the lightest engine you have.

An Enya is a good RC, sport, and stunt engine.  Despite the beefy look, they have a reputation for failure when pushed to do combat duty.  I blew up two out of four that way.

My best recommendation is to bench run the engine/tank/prop/fuel combo before installing it in the plane.  Back in the day, a lot of matches were won by the lone contestant whose rig worked.

I built two Midwest Hornets, didn't like 'em much.  The Wasp was infinitely better.  I might build a new one if some plans surface.   The Equalizer was a modern rendition of the old design.  Very accurate 'cept the plastic covering.  If I build another OT combat, I silk it like the lord intended.

Back before I got into competition I used to build the combat planes of the day.   The T-Square was my favorite.  Flown with McCoy .35 or K&B .35.   Combat Cats were first to use crankcase pressure.  A few years ago flew a Big Iron with a Johnson CS.   What a rush for an old man.  Wind did not bother us one bit.

It doesn't matter what engine you put on the old combat ships, as long as it's not electric.     And, yes, Barry is one of the best plans providers.   I have built several planes from his plans.

Hi Paul,

Well, that paints an interesting picture (riding bike with combat plane with its engine running)!!

I used to ride my bike carrying a fishing pole but that ended when the pole went into the spokes!

-Chris