It's the BW designation as far as I can tell. Yes the front part is a muncie unit, on the later O/D units, after 1966 thru 1987,the front portion is the three speed Saginaw unit, fully synchronized. The O/D unit itself (the tail section containing the governor, solenoid and planetary gears) is designated "R 10 H". Put the Muncie, or Saginaw together with the R 10 H, and you get a T85N. The R 10 H was put together with other trannys of different manufacturers (F##D, Mo*#r, etc. and given different designations). BTW, if you look around on the web, you can find an article, where a guy took a R 10 H tail and with a few modifications, was able to mate it to a FOUR speed Saginaw, with gear splitting in all four gears. Which you can do with the three speed version if you wire it correctly.(Gear splitting, that is) Again I refer anyone with questions about this tranny to this site
http://www.speedprint.com/Deves50/OverdriveIndex.html (fixed link)
