Yep, the milling of both parts is what's causing you some problems. Nothing much you can do about that except change around pistons and cam to match. Wow, 123cc's still?? That's a pretty big chamber. Im not extremely familiar with those pistons...I know they're a popular one to use, they are a medium size dome, aren't they? Which valve did you have that clearance on, intake or exhaust? And what were your clearances from .020 BTDC to .020 ATDC? You can gain some clearance by advancing or retarding the cam...depending on where you need it. But when you gain on one valve, you lose a little on the other. I know on my engine, Im almost 0 decked (.005), and heads have been milled about .040, so I have the same problem. I have plenty of intake valve clearance cause the pistons have large valve cutouts, but Im tight on the exhaust. I advanced the cam to gain more on the exhaust, and the cam I just ordered was custom ground to help with this same problem. You can work around it.