I hope this helps you. I believe what you have is a VIN derivative. Your engine probably came out of a 1971 Oldsmobile assembled in Lansing, MI.
This number should take the form of "35Mxxxxxx" where:
3 = Oldsmobile division.
5 = year of manufacture (8='68, 9='69, 0='70, ..., 4='74, 5='75, 6='76, etc).
M = location of manufacture (M = Lansing, B=Baltimore, X = Kansas City, Z = Fremont, CA, etc).
xxxxxx = last six digits of VIN of car that motor originally came in (original car's sequential production number).