360 runs strange, lifters??

It's about time for an oil change, I might dump some Marvel Mystery Oil in it and see what happens. The truck sat without running for 10+ years according to the seller when I bought it, might have some gunk in the lifters that never worked its way out.

I have some new valve cover gaskets to put in, I'll check if the new head gaskets I installed back when I put freshened heads on it block the lifters from being able to be removed. They were the standard Fel-Pros that come in the full engine gasket set, 8553PT is the part number??