[Kurt S]

I'd guess that for some reason they pulled unique engine code for the non-smog Canadian engines. Instead of plugging the manifolds at the assembly plant, the engine plant shipped them with non-drilled exhaust manifolds.

Any of these # coded engines still have the original manifolds on it to confirm this theory?

GM of Canada microfiche:
The engine codes are only on the Canadian built vehicle records. Imported vehicles don't have that info.