Another pulley question

for a stock alt I would suggest a 78 amper listed for a 85 M body & as mentioned space it fore/aft till one of the pulley grooves lines up (preferably the one closest to alt but this ain't a dealbreaker) or if aesthetics is desired have your alt shop install a single groove pulley & same thing, washers/spacers to get belt alignment dead on. there are 2 sizes (diameters) of 2 groove alt pulleys and you want the smallest dia (dont remember the dia's right offhand and not sure if the single goove pulleys you are after have those same 2 different dia's available. Mopar alts have low rpm output issues and the smaller pulley will help with that as will a large crank pulley (if your WP pulley is small enough to accomodate it). Speeds the WP up also, generally a good idea as long as high rpm cavitation ain't happeneing but an anticav plate takes care of that & is a good (cooling) addition.