Gasket cut from a magazine cover? You call that a problem? I heard the story once of a guy whose CZ had the whole barrel come unbolted while he was riding. He pulled up to the rest of the riders and said the bike was "acting kinda funny." They looked down and saw the whole cylinder rattling up and down by quite a lot (didn't hear an actual number, but I got the impression it was something like 1/4 to 1/2 of an inch, sounds a bit crazy). Understandably, everyone panicked and waved wildly for him to shut 'er down. Imagine that that must've done to porting and compression, no matter how little movement there was. That was pretty much all the proof that anyone needed that CZs were tough as hell.
That would be an urban myth, as the slightest hole in a base gasket has it sucking air and free revving it's head off.
To answer the question you have described what is termed 'negative deck height' (positive being the piston above the cylinder deck @ TDC)some cylinder heads(like the one pictured in the article ,usualy European brands) have the head sitting down into the cylinder. What really matters is the height of the exhaust port open from TDC.
