Easy question-- engine serial number
Posted: Sat Nov 01, 2014 4:46 pm
Where is the dang thing? 
Depends on the year. I found some info that might help, with the source link below.
1964-67 V-8 Engine:
Code is stamped on the right cylinder head. Unfortunately, this only applies to what was originally the driver's side head. This code consists of a prefix letter (330 V-8=T (1964-65) or W (1966-67), 400 V-8 = V), then a production sequence number, followed by a suffix code letter (L = Low compression, E = 2-bbl export, G = High compression, H = 4-bbl export). A 2-letter code on the oil filler tube identified the engine.
1968-later V-8 Engine
Have the last six digits of the VIN number, the year of the block, and the assembly plant stamped on the driver's side of the block below the cylinder head. A 2-letter code on the oil filler tube identified the engine.
You can use the VIN derivative number to ID the year. For 1968 and up blocks, this number is located on a pad just below the cylinder head on the front left side of the engine. This number will be stamped on a machined pad on the front driver's side of the block, just below the deck surface. Typically it will be covered with a power steering bracket or something, below the number one spark plug location.
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).
http://www.442.com/oldsfaq/ofeng.htm#Engines%201964%20-%201990