this is a Muncie m21 and what to look for as a stock m21 Borge warner box looks very similar less the diamond and numbers proving a true rock crusher as these numbers are traceable Muncie codes and can tell you what car it came out of, this box from 71 corvette. all Muncie boxes stamped with numbers on all casings and dont be scared if numbers different on housings as a lot of these boxes were reconditioned and some numbers not same as front housing to back.. just MAKE SURE YOU HAVE A DIAMOND STAMPED ON BOX and is real mcoy. AND dellow engineering has convertion straight up kit if you need one.