I have 1957 and 1959 261 engines from Canadian GMC trucks both stamped serial numbers start with a "W". The "M" inside the raised square on the right side of the engine indicates it was cast in Canada by McKinnon industries and the captains bar indicate a 261 engine. Solid lifters its a truck, hydraulic lifters for a Pontiac.

1954 Chevy 1300 engine 235 (1959)
1955 (first series) Chevy 3100 engine 261 (1957)
1927 (other brand) Model T- engine 327 (1968)