i need help w/duster engine

.600 lift on stock length valves and uncut guides will not work. The piston to valve clearance isn't your biggest worry yet. You will need to address the retainer to valve guide clearance and valvespring coil bind first before you can get to the piston to valve clearance. Which by the way is not going to be enough either if it even turns over.

That is way too much cam for that engine anyway, besides that you'll probably need to block the oil to the left bank lifter galley and tube the right bank galley and redrill the oil feed holes to the mains because roller lifters will uncover the holes used to oil hydraulic tappets (not needed on solid flat tappet and roller cams) causing a severe loss of oil to the crankshaft and the severe, nay, catastrophic engine damage that will ensue.

Those heads are probably not going to flow any more air past about .480 lift anyway so anything over that just screws up the air flow and you'll end up with severe exhaust reversion back into the cylinders and intake path. The engine will make less power and run like total crap.

If you need any more reasons not to install that cam just ask, I have plenty more.