Panic,
A few minutes of looking at other sources shows that
1954 Truck Shop Manual also lists different part numbers for the 235 and 261 engines, but the numbers seem to be different than the numbers in the 1955 shop manual in your post. However, the
1929-1957 Master Parts Catalog shows the same numbers for all 235 and 261 applications. Of course, there are still the four types of rocker arms. The next step would be to look at the rest of the shop and parts manuals, and at a lot of rocker arms.
