Most all the pumps ( mechanical ) that I have installed in engines, have some spring pressure on them while bolting them on. Maybe I just get unlucky and hit the lobes every time, but you should feel the resistance from the pump arm when bolting to the block. Fuel pump lobes wear off the cam just like lifter lobes do. You should be able see in the opening with a light and mirror or inspection camera and see the lobe. Have someone rotate the engine while you look. They are not big lobes, but you should see if it's damaged or missing.
Adding a small electric pulse pump is pretty straight forward, no need to pull mechanical pump off or apart, the electric will push fuel right through the engine driven pump. Look for one with 2- 3 psi output, anymore and you could run into needle and seat issues which leads to flooding. Use a safety switch with manual override for priming. Safety switch allows pump to run only when oil pressure is present. You will have to get specific information about your engines oiling system from someone else, I don't know much about the early engines. The Chevrolet Vega ( from the 70's ) used an oil pressure/fuel pump switch which is the common one everyone uses now. Most parts houses will be able to get one, or shop online for Vega oil pressure switch. DO NOT just wire the pump to an on/off switch. For a primer switch, use a push button only so the pump only works while holding the switch.
