looks like im pulling the motor apart already

With -17.5cc dish pistons, zero deck, 62cc chambers, and typical .040 gasket his compression is 10.5:1 which is more than enough to detonate with ANY camshaft if he got a bad batch of pump gas or old gas...
And that's if his timing was perfect. Guys don't realize with iron heads once you go over 10:1 even with good quench you have the potential for detonation using PUMP gas. And where the cam was installed has an impact on that as well.

You say his machinist told him it's zero decked...CHECK it yourself!!

I'm just sayin.....