The QF carb is the problem, they have a very rich idle circuit.
A Holley 4777 650 dp would work good out of the box. You can fix the QF carb but it takes some time to get it right. The jetting on a Holley 650 should be pretty close out of the box, also the FST 650 works very well also that's what I have on my 350 Vortec engine right now. Floats were set right and the idle mixture and speed settings is all I tweaked. A very good carburetor.What would be a good easy tunable great outa the box carb under $500? . Aside from ls swapping it I’m hoping a carb swap would do it. Worst case changing the jets.
Other than cracks they are great heads, best production head GM ever made for a SBC.Just switched to an avs2 and it does much better and no fuel smell. I switched to autolite 3926 plugs. Any issues running these in Vortec heads?