The K&B engine is of little relevance to the Fox. Most of my Foxes use a head shim. They are often an aluminum, so there is always a metal to metal contact in the head sealing area. If you don't have piston the head contact the head gasket or lack there of shouldn't be an issue. It isn't an issue as far as fuel draw.
You should be able to get the engine to "run" if the crankcase is properly sealed. Power, over heating and throttle response are all issue we can work on after you get the engine to run.