If you're using a head gasket with 0.039" compressed thickness, you should still have plenty of piston to head clearance with the iron heads.
IIRC, the chambers are about 0.100" or more deep.
I've got that same cam in my 340 and love it.
My pistons are 0.020" above the deck and I have plenty of piston to valve clearance. But the KB pistons have pretty generous valve reliefs.
That's the clearance you need to be concerned about.