1970 Swinger 340 resto

I am saving and/or collecting original parts for the car in case I want to put it back stock. Transmission, rear end all body etc were numbers matching but the block. A 318 was installed with the stock intake and heads when I got it. Haven’t found out what happened to the block. The original owner sold it and then bought it back, maybe more than once. All he knew is that he sold an orange car and bought back a blue one.