So I wanted some thoughts from someone who may know.
I have an incredibly original 1970 cutlass supreme. I noticed that all the date codes match at the time of build based on the build sheet. Engine, alternator, heads but when I looked up the engine VIN I got 30e173291 and the vin 336870e205831. Is it possible that early in its life maybe it blew up and a shop may have swapped a short-block and added everything from the original motor maybe?

 

Yes. It's possible. May have been a fluke to get a block so close to your VIN, and it's also possible that both engines could have been built in the same time frame and could be original heads and junk to that particular block. Sometimes karma works out. More than likely only the block was donated to your car, and the peripheals are still original to the car. Who knows for sure except the original owner? If the date codes all check out, it's hard to determine.

 

And if it presents as factory and is not a particularly rare and desirable model, does it really matter all that much?

 

Have you checked the transmission VIN derivative ?

 

It's not only possible but highly likely. Why would someone pay to change those parts when all they needed was a short block. Of course, since that's a used short block from a different car, it's kind of irrelevant as far as value is concerned. Also keep in mind that there are thousands of parts that have the correct date code and casting numbers for a given vehicle, but only ONE numbers matching block and trans case. The fact that the date codes are within the accepted range doesn't prove anything.