Not sure the exact size, I can post a pic when I get home. It just has to be big enough to cover the hole. 1/2" maybe? I think this is really a non issue and a simple mod really. Much less of an issue than trying to get those wrap around mufflers to hang on with the side exhaust engines. With those a clamp has to be fabricated to attach the other side of the muffler to the engine. That is a notorious issue.

When looking for an engine, you need to decide what is the most important issue for your application? If you need a small footprint, far and away DLE is on top there, with rear intake, rear exhaust, and angled plugs.

I actually prefer mag engines and spring starters, so when they fit, I like Zenoah. The side carbs pose problems with my warbird projects though. Although I do have a 90 degree manifold for my G62 that lays it flat on the side of the engine.