4-Door with 340 from the factory?

People did/do all kinds of day one add on's and changes.

They still do with modern musclecars. But back then you could do whole motor changes much easier because everything wasn't so integrated.

I have dealer and original owner documentation of an 454 LS6 being put into a brand new 70 1/2 Camaro SS 396 325hp car. Owner saw it could be done in a magazine. He called the Regional GM Rep (even have owners notes).

We looked at it 38 years later and it looked stock. Even the date codes; which make sense because it was done in 1970.