Brakes and noises...

First question, how do you tell what size drum you have to replace the shoes if they are so rusted you cant read the stamped size? Would measuring from the inside edge to opposing side be accurate? Second, as long as the inside of the drum looks good (no scratches, scores, or chunks missing) does it matter that the outside is rusty? And finally, there is this rapid clicking noise under my jeep whenever i'm moving, faster or slower as the jeep gets faster and slower, i had the same exact clicking sound in my 93, and now i have it in my 94. Could this be bad u-joints? Ive tried to move the d/s around to test like everyone says and they always seem to be fine, no play...for the price maybe i'll just replace them anyways...anyways, any suggestions appreciated. Thanks!