No way to tell for sure about the 4" crank. Merc heads aren't a guarantee. Don't ask me how know. Looks like it has a Holley 94. Not positive but I think Merc's had a teapot but things might be different with Canadian flatheads.
M-6 is a pretty good sized truck but as noted above, without pulling a head to measure stroke no way to know for sure. Parts have a way of moving around over the years. Thought they were using aluminum heads in Canada around then. Interesting!
im sorry guys, i should have given more info. this is in a 51 mercury M6 truck. truck was my grandfathers. 20,000 original miles. the truck has never left the farm, and has never had any work done to the engine. that is fact , not guessing. purrs like a kitten. so im tossing around the idea of useing the engine in a rod. i expected to see 8BA on the heads. im not about to pull a head to find out for sure however. ive never seen a teapot carb on ANY of these bigger trucks up here, and ive seen a lot of them.
Leadbeater, given what you have said, it may be worth digging into old advertisements or search out a manual. If you use the existing heads and leave it together, most will think Mercury 255. FWIW, I left Mercury heads on mine.
Very nice old truck. I think I'd restore it as is, and find another engine to build a rod with. Maybe even turn the old farm truck into a car hauler for the rod. I like the "Made in Canada" on the head. But, as they say, it's your truck (car). I am Butch/56sedandelivery.
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