[FirstOwner69]

I agree that you need a twist on cap. Probably the LMC # 30-4122. I'm no expert, but I don't recall that type of filler used in the intake after the 283s and 327s and implementation of PCV valves. Prior to PCVs that type of filler (but without the restriction and notches at the top) that I recall seeing used a push on ventilated cap similar to the LMC 43-4350-C. What year and displacement is the engine? Is the intake original to the engine? Does thit have a PCV valve?

EDIT: My original 350 with a hole in the valve cover uses a twist on cap. The diameter of the hole measures 1.20 inches (slightly greater than 1.50" at the notches). If that's what yours measures, I'd again say you should get one like the LMC 30-4122.