The serial number is likely buried under that paint, and unless you have your heart set on repainting it, I wouldn't suggest sanding down to it.

That lug set was not uncommon. It bears similarities to my '76 Team Professional, but the seat stay treatment is very different, your frame has internal cable routing, and an extra stylistic element on the fork. I don't have anything to contradict bulldog's hunch, but I think the other information that might help establish the identity are the dropout manufacturer, the bottom bracket threading and the seatpost diameter.