[rotorwrench]

The Mercury 255 engine used the larger clearance volume heads to give a similar compression ratio to the smaller Ford 239 V8 engine for reliable operation. The Canadian Mercury M1 pickups came with a 239 so it would do better with the 8BA or EAB heads. The 8RT heads were developed to lower the chances of detonation while under extreme loads. The M3 and possibly the M2 would have had 8RT heads as stock from 1952 on. I'm not sure about the M1 in 1952 but they also likely had them. Earlier F1 and M1 engines would have had 8BA heads up until 1952 when they were superseded by the EAB heads for cars. Trucks likely all had the 8RT heads after 1951. Canada did do some things different but the use of the Mercury car 255 for trucks was not a standard thing even in Canada. It was usually optional in trucks larger the F3. Trucks larger than the F6 would have an engine derived from the Lincoln 337 design V8 until 1952 when the big Lincoln type Y-blocks were incorporated in the Big job trucks.

If a person put together a 255 engine by replacing the crankshaft and pistons the the 8CM heads would not be a bad thing. The Mercury had its own cam shaft and Holley 885 carb but the Ford stuff would work on it.