A 500" engine with an 850 carb will likely cruise on the main circuit not the idle circuit. Although the OP should check to be sure. But he said that his idle is good, so leaning his IFRs is not a good place to start in my opinion. Besides, the main jets are the only items that screw in. Everything else requires drilling and threading in order to adjust. (Of course there are always wires.......)

The PVCRs do not have to be drilled at first. The mains can be dropped down how ever many sizes you wish and then the cruise A/F checked. But if the mains end up needing to be sized down, then the PVCRs will need to be enlarged to compensate.

Again, I think that the easiest and best start would be to disconnect the secondary linkage, drop down several main jet sizes and test drive the cruise. Just be aware that the power circuit will be lean until the PVCRs are opened up.