Yes it’s a big block a 383. I tried reusing the old valley pan when I reassembled it again and again. I’ll order a new valley pan(what brand) and maybe I should use a special type of intake gasket possibly between the intake and valley pan? Should I also use the copper spray and spray all meeting surfaces with the copper spray and lay down some oil and gas resistant permatex?
I never reused the valley pan always put on a new one nor did I use any sealer on the head or intake surfaces, just on the ends of the valley pan between the pan and the china walls to prevent oil seeping out - never had any vacuum or oil leaks.
When you have it all apart and the surfaces thoroughly cleaned take a straight edge and a feeler gauge and check the head and intake surfaces for flatness.
Were your cylinder heads milled by any chance?