yeah this thing is nuts, having the bridged transfer opens up a lot more potential.
with that crazy shimming issue, a shim and a countersunk head would be the way to go for sure. i prefer cutting the cylinder down on a lathe, but i know not everyone has that technology.
it would really be ideal to just find the right damn piston, or a better one, something with one ring.
I know a lot of KTM cobra/junior/senior50 shit is very similar to puch, anyone looked into that? If you really are gonna put the beans to this thing you probably ought to have a real nice piston not some generic pot metal taiwan junk.
just guesstimating off that port map, i would say 12k no prob with the exhaust wide like that. whether it can do that running 18/36 gears i'm not so sure, but we shall see. drew human bean would be the one to talk to, he has the sickest AJH athena that i know of, i think he was getting near 70 on it last i heard.