Squareback vs round back alternator?

Square back is a better design, and some amp ratings charge better at low rpm. 45amp I think. Something that seems to be prevalent with rebuilders is MISSING OR IMPROPERLY installed brush hardware/ insulators. BEFORE you wire it up, check between the two brushes (field terminals) which should show a low value of resistance. Then check each field terminal to the case and it should be "open" (infinity) resistance