I've never seen part # assigned to the first gen rifles, other that the number in the schematic followed by a description such as left hand, or short action.
Unfortunately, I have very few first gen parts at all. I haven't worked on many first gen guns to even document some of the features or differences, but the majority of the ones I have worked on all seemed to be lefties, for some odd reason.
They only made like 50 some odd thousand of these, so parts are gonna be like chicken lips. Even if you can't find a magnum magazine, I would still try to make a 30-06 mag work if you find one of them.