The most info I ever found on the dubbing was in Sam Arkoff's biography. Check out the "US Dubbed Release" section at this page:
http://www.madmaxmovies.com/films/mad-max/index.html
I believe the dubbing studio used was named in the book, but I didn't put it on the page above (which really does need some other updates too...!) From memory it was "Titra Studios". A few people have thrown me a few names over the years (David Hedison keeps coming up for some reason, although as per above, apparently not), but no one has ever been able to get confirmation from anywhere. Certainly a couple of voices do sound familiar, particularly against some US TV / Cartoons from the same era.
As for lengthy credits, up until basically the 1970's, most films didn't have the kind of credits we see today. It was really just the main players, and that's it - like you say, who really cares who makes the coffee? The first Mad Max was the same, then for Mad Max 2, the credits were quite different. One of the guys involved with the film at the time once mentioned that Byron Kennedy had stated that he "wanted the longest credits of any film, with everyone in there, right down to the guy that mops the floors"! The theory is, the bigger the credits list, the bigger and more impressive the production looks - I mean, look how many people were involved!