Yes. If you run an LA style timing cover and accessory belts you can run the fuel pump eccentric and a mechanical fuel pump.
A Magnum camshaft with a short snout will require an adapter from Mancini Racing or Hughes Engines to mount the fuel pump eccentric.
An LA style long snout camshaft will mount the fuel pump eccentric with the bolt and washer setup from your old LA engine.
If you found an early Magnum block that is drilled for LA oiling you can use the rocker arms you already have, and you can install LA cam bearings and an LA camshaft drilled for LA oiling and with a long snout, which reduces all special considerations.