Update:
re-assembled the valve train, torqued properly. Performed a compression test on 2, 4 and 6. all came back equal, so that was hopeful.
I pulled the exhaust manifold and sure enough. bad spot on the gasket at # 4. So that's the noise I'm sure.
I happen to have 1 manifold gasket, but when I started to torque the bolts/nuts to 30 ft/lb, the rear nut/stud stripped. then one of the long nuts did the same, so I gave up and ordered some replacement parts for that. Now I wait. I bought the 68-71 C body kit, which isn't exactly correct, but has what I believe are enough long bolts to do the one manifold.
Thanks for all the advice, I'll update once I get the kit and install it. The fuel in the oil is a different matter...