I am thinking galley plug, did you put a little nick in the block after you installed your galley plug to keep it from coming out? Maybe your
oil pump is loose or it is the relief valve. As the others stated pull the valve covers and spin you
oil pump counter clockwise with a drill, I think the 302 base engine takes a 1/4" drive shaft on the
oil pump. Do not start your engine again until you have this issue resolved.
Keep us posted on what you find.
Clois