Interesting! Thanks, Ted.
I'm often surprised at the re-engineering that is done during the life cycle of a product. I would have expected the '54 Merc 256 and the '55 Ford 272, 'Bird and Mercury 292 intakes to all be the same. The casting number change suggests that something like intake runner sand cores were changed. Likely, there was ongoing dyno testing of the engine as cubic inch displacement was increased. That said, I'm disappointed that the rockerarm assembly oil deflector trays (?) and the timing set drip tray were eliminated before the (?) '57 model year as 'not being necessary' or at least not being cost effective.
I'm still puzzled that the late 292 truck engines with the forged cranks used a different connecting rod length than had been used for so many years in the 239, 256, 272, and 292s. Additionally, rather than using the 312 connecting rod which was the length they went to for the HD 292 truck engine, they designed a new beefier connecting rod. $$$ to do that. Additionally, opting to use a shorter connecting rod for the HD 292 truck engine required a change in the location of the piston pin. Again, $$$ to do that. I assume that the decision to use the shorter connecting rod for the HD 292 truck engine had something to do with a mathematical calculation regarding piston dwell time at TDC or torque at some particular engine RPM. I'm guessing on this as my engineering insight is rudimentary at best!
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York