Let me clarify the above about the 2 and 3 letter coding. Up to 1981, GM used a 2 letter code for engine exhaust emission certifications. After that, they used 3 letter codes. 81 was a weird year, like diesel cars still used 2 letter codes while gas V8 in USA used 3, and Canada cars still used 2 letters. In 82, they pretty much used 3 letter codes for every combination. Probably ran out of 2 letter code configurations.
mok616 has an 86 Cutlass, so even though it's a Canadian car, it's got a 3 letter emission code. Thus,
ranllett has a 78 with a 305, his 2 letter code is different than an Olds engine in 1978, even if it was a 305. They seemed to change the appearance of them between brands as well. During the late 70s, Chevy liked to use silver a lot, and Olds used white for the most part.
There's seemingly about 32,000 (exaggerated, but not much I bet) different combinations of engines throughout the years, and MANY of them are different. Now, sometimes you'll get the same coded engine emission certification on some other brand or model with the same engine/exhaust configuration, but a slim chance. And, depending on the EPA requirements, they tended to change the lettering configuration each year. For example, the 84
H/O and 85 442 used the SAME EXACT DRIVETRAIN. Same ECM box (different prom number due to EPA, but I'll bet same info was on it), cam, heads, block, internals, intake, distributor, and carburetor (it was restamped 5 over the 4 in the year- only difference). Yet all the junk is coded differently for the emission label. Even used the same part number air cleaner and exhaust components. OZ transmission with the same calibrations, and 3.73 rear gearing with the same Goodyear 215/65-15 tires. Emission label HBM for 84
H/O, but 85 442 used SBJ. Basically a replay of 1979
H/O -1980 442. Go figure.