Jerry is correct (as usual)
1/2 ton drums are the same front and rear. They're not riveted, however, but are held on with the lugs swaged into countersinks in the holes. The shop manual says that the lugs can be pressed out without removing the swaged metal from around the lugs. It does say to re-swage the lugs, but I think you could get away without doing that. The lugs built for swaging might be hard to find, and you need the tool as well.
[on edit}Whoops! The above only applies to '51 and above.
'40-'50 brake drums are different front and rear on 1/2 tons.
Fronts are PN 602432 and Rears are PN 601985
to the OP, some brake drums have the maximum service diameter cast into the drum. I've seen it before on the outer rim. You might check to see if your are marked.
