I have found that there are two general styles on trucks.
One style fits 216 and 235 (perhaps 54-55 261?)engines from the first production up to the 54-55 transition year.
The other fits 55-62 235 and 261 engines. The top of the cover has a slight V-shape where the older version is flat. I think a safe generality is this type is used on all engines with the later style water pump.
