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From the April 69 Service Bulletin--

Service usage:
The following system will be used to identify service engine and transmission assemblies* including replacement parts. Manufacturing plants will number each service assembly as it is produced. The first letter will designate the G.M. Division which produced the engine.
C= Chevrolet
B= Buick
L= Oldsmobile
P= Pontiac
K= Cadillac

The Second letter will indicate the type of unit "E" engine or "T" transmission. The number following the letter will designate the model year "9" for 1969. The last five digits specify the service replacement unit sequence number.

Example---CE900175 designates Chevrolet Engine--1969 Year and the 175th unit produced for service at Flint Motor Plant (L-6)

NOTE: This numbering system applies to service engine assemblies, partial engines, fitted cylinder cases, cylinder cases, transmission assemblies and transmission cases.