Pulled the valve covers again to check for any sludge as I'm still slowly losing coolant. I should have gone ahead and pulled the rockers to check for Castech as I've got 706 heads. No signs of any sludge at all. Also none of the oil drain holes were clean as the TSB suggests for a problem. Hopefully I don't have a tiny crack anywhere.
Idle is still kinda rough, so definitely on to intake manifold gaskets. Time to order up all the goodies.
I think I'll also get some UV dye to add to the coolant. I'm just a bit perplexed because I'm not sure if I still have Dexcool after I had the waterpump replaced a couple years ago. I saw there's specific dye for dexcool from Delco.