[tekuhn]

Here’s my summary of what’s been learned from this thread:

SOMEBODY installed a ‘66 tripower and a ‘58-‘62 camshaft on a ‘67 428 engine, AND transplanted the engine into a late ‘70’s Firebird prior to your purchase of it. The engine block has some numbers stamped on it that the factory did not do. No one has been able to produce pictures or documentation of engines with similar markings that might help determine who made the markings and what they mean.

You have received numerous responses from people who have been in the Pontiac game a very long time and who have been around some very exotic factory rare pieces, and all of them are giving their opinion that what you have is a nice 428 that someone did some parts swapping on. I tend to agree. The biggest reason to me, is the camshaft. Why would a dealer install that old cam when the current tripower cam (068) would have been readily available and provided higher performance?

As you surmised, unless you can find original owner of the original car, you will never know the story.

No rudeness is intended.