No such thing as a leftover A block 318 poly in 1967. Chrysler Canada built A block poly 318 engines in 1967 for Canadian-built C body Plymouths and Dodges as well as Canadian-built Dodge and Fargo trucks..
Chrysler of Canada would not have the tooling for the LA 318 ready until the 1968 model year, You can tell a Canadian 1967 A block 318 by the engine number (located on the front of the left half of the block just below the head).
The US-built 1967 wedge LA 318 engine serial numbers started with C318 (C for 1967) while the Canadian-built 1967 poly A 318 engines started with CC318 (First C for Canadian and the second C for 1967 model year.)