I don't know about Canadian '53 heads, but all US '53 heads had 2 acorn nuts holding the valve cover on (there were no holes for a 4 bolt cover). Maybe your original motor is not as original as you suspect.
Carl

Last edited by 52Carl; 02/14/2016 3:09 AM.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission