[Arschloch]

Otto used the Hitchcock one. I think that seems to be a safe bet,
Regarding clearance, I will ask him what he used.
Typically, .005" would be okay with a careful break-in on an 87mm forged piston in our application.

Regarding valve to piston clearance, you really need to check your actual engine because of variation in parts manufacturing. Try to get .060" on the intake for valve to piston. I use a soft clay pad 1.5mm thick on the piston crown and turn the engine slowly by hand, and look for a ding in the clay. Then measure the clearance from the bottom of the ding to the bottom of the valve relief in the piston crown.

It's JE piston I put into my GT. It's actually from Kevin although I got it second hand from a forum member. If baker still has it I don't know, anyway it's a  good piston and it wasn't the cheapest. It's flat top and weighs about 5% less than the stock GT piston - good if you wish to rev. the bike little bit more than to the stock rev. limit. It also seams to make less slapping noise than stock and has exactly same clearance. It does look about the same as the one listed at HMC's page just without the valve relief. I did cut a custom relief in it for the intake valve.