The gasoline engines don't use as MUCH oil but there's still some. So it's still prudent to seal off any pushrod and fuel line feed through openings to keep out the oil contamination.

For any and all glow engine models that I've ever done it's just simply something that is done.

For sealing the fuel line feed through points I always drill the birch ply and smoothen out the holes with a nice rounded flare on each side. I size all this so the silicone fuel line passes through with a good amount of firmness. But open enough that I can push the stub of tubing through then pressure seal it to the firewall passage by inserting a stub of brass tubing to force the silicone out tight to the wood.

The stub of brass tube then becomes the attachement point for the line to the actual engine.

I'm guessing that the equivalent should work for a gasoline engine. Or just by the threaded feed through fittings.