High mileage slants can have the fuel pump enteric on the cam worn out. There is a good picture of one in Dutra's slantsix book. If you pull the fuel pump you may be able to look at it on a pickup truck.
One of the problems is today no one wants paper manuals the old Chilton's and Motors Manuals had a lot of basic diagnostic techniques in them. No one knows how to work on points and carburetors any more. Sad.
Tip most of the guys that know how to work on this old stuff are over 60