As great and wonderful as this H.A.M.B. 261 thread is, i have to clarify one big thing............. the American and Canadian 261 six in liner motors are different in some very key ways. Much of the information on this site does not pertain to our Canadian 261's. The main key differences are that our Canadian 261's had a hydraulic valve train and the American 261's were solid lifter valve train. The American 261's had a full oil filter system as of 1957, our Canadian 261's had an optional by pass oil filter system. The American 261's were a Chevrolet large truck engine that was an optional motor over the 235 Chevrolet truck engine. The Canadian 261 motors were only offered in Canadian Pontiac's from 1955 to 1962 as an upgrade over the Chevrolet passenger car 235. The Canadian 261 shares the American 261's stout bottom end with thicker rods, they both have the steam holes in the block and head and they both have the higher lift cam, the higher compression and the larger one barrel carb. All these extra's the 235 Chevrolet six never had, except the Corvette 235 six of 1953 and 1954 had the higher lift camshaft. I hope this helps. Cheers. George.