Small block intake

Swapping out that old lazy cam is going to be your biggest bang for the buck in a all stock 360.
Even with the OE 2 Bbl and intake.
Something like the old Comp 260 ([email protected] and 110° LC) would give you a much better foundation to build upon, so if you do make a manifold change, it will pay off in dividends.
The new split pattern Cams would be even better.