Hydrolock???

IMO these heads have been getting hot over the short time since rebuild. It's especially noticeable in the heat cross over area as the baked on oil suggests.

Were the head bolts torqued with a quality wrench?
Were the head gaskets Felpro "perma-torques"?
Were the head bolts "re-torqued" after a few hot cold cycles?

I will post a PM I sent to another member shortly
But to answer your specific questions

1. I would hope and guess so. Engine was rebuilt by a trusted machine shop for thirty years of my uncle who owns a shop.

2. I dunno but I imagine they were whatever cheapy felpros because the master rebuild kit was the last one the shop could order from their distributor and it was only like $150 on super closeout price.

3. I doubt it. I know I didn't retorque them. The shop just rebuilt the motor and delivered it to my tranny guy who was around the corner so tranny guy could install accessories and button everything back up.