This link on the Canadian engines I think throws up a lot of interesting information which supports the points Guy put forward, somewhere I have and at the moment can't find a lot of information on the parts and specifications of the 313 and 318 units which I came across when trying to help someone find parts for a 313. I found out some years after my 313 was rebuilt that the heads would have fitted a 318 block which would have been a cheaper option. The 313 after the rebuild ran beautifully and cemented my admiration for these V8's
especially after managing 17000 miles running mostly on seven cylinders because straight out of college I couldn't afford the engine rebuild. Like Nicks engine when mine had been re bored and fitted with a set of high quality pistons it too was probably approaching 318 cu ins.
Geoff.
https://www.allpar.com/threads/canadian-engines.229915/