Yes it does matter. The horsepower went from 285 to 325 HP from 56 to 57. This was due to an increase in the compression ratio from 9.75 to 10:1 . The Eldo's did even better on HP,but that was carberation.If the engine stayed at 365 cu in the increase in comp.was due to a change in the heads ,rods,pistons or crank. I checked only the heads changed.
To tell them apart without part numbers can be done with casting numbers. But I don't have a full list,so the other way is valve diameter. To do it this way you need to just measure the diameter of the heads of the valves. Measure at the point where the valve seats to the head, not the outer diameter of the forging. 1956 inlet 1 3/4 " ,exhaust 1 9/16" : 1957 inlet 1 7/8" ,exhaust 1 7/16".The 1957 exhaust being smaller seems odd since racers are always trying to make their engines breath better ,but I checked two sources and they agree.
Be sure you watch the the push rods and lifters on this engine. They were changed mid year 57 . It won't matter if you use early or late as long as you use pairs.Warren
