Reference the 20 thousandths clearance, I assume you mean 2 thousandths (0.002"). It will work but don't expect 20'000mi out of them.
My last set of pro x pistons were fitted with 0,0016" clearance (1.6 thousandth), I was very gentle with the break-in process and now have 3500mi on them. While I may not recommend such a tight clearance for others, i would be confortable recommending 1.8 thousandths clearance.
One of my bike has +0.005 clearance of forged pistons and still has good compression and is quiet once I get cruising, the other website doesn't like it!
My last set of pro x pistons were fitted with 0,0016" clearance (1.6 thousandth), I was very gentle with the break-in process and now have 3500mi on them. While I may not recommend such a tight clearance for others, i would be confortable recommending 1.8 thousandths clearance.
One of my bike has +0.005 clearance of forged pistons and still has good compression and is quiet once I get cruising, the other website doesn't like it!