Will using the lube that comes with ARP bolts/studs cause stock head bolts to be overtightened? I know that ARP has different torque specs when their lube is used vs oiled threads. Just wondering if it would be a bad idea to use some of the ARP lube I have left over from some previous cast iron motor builds.

Dunno what the ARP stuff is, but it should be fine to use since the final torque step is designed to stretch the head bolts anyway. If it'll make them easier to turn you'll just have an easier time getting that last 90° turn on the bolts.

Factory service manual says to use engine oil on the head bolt threads and washers.