JW,
Using
GMpartswiki [
gmpartswiki.com] search engine link, GM# 8616710 comes back as:
Parts Group: 4.158 Gear spacer, trans front unit, internal (applicable to 1956 Oldsmobile "O" HT (Hydramatic Transmission) and 1957 HT (Hydramatic Transmission) applications - just one of many different thickness spacers noted)
http://www.gmpartswiki.com/getpage?pageid=2082The GMpartswiki search only returned one manual - 1961 Oldsmobile P&A Catslog (PA-93) dated Dec 61 and Revised Apr 62 as the lone place this part number was listed.
I will donate the 1000 points to what ever needy cause you deem appropriate.

Dan