Ok, so I purchased some parts based on suggestions I recieved in this thread:
http://www.airsoftcanada.com/showthread.php?t=72175
However, neither the tappet plate or the cylinder head fit. The tappet plate I could file slightly to fit it in properly.. but the cylinder head doesn't seat right and the mechbox won't even close. It looks like the holes on the side of the cylinder head that match up with the ones on the mechbox are too small (tappered too much). Any suggestions on how I could fix this?