The 1962 is the other 925 and has the small port. Anecdotally, I have seen many more 261's with the small port than without. Before today, I didn't even know there was a casting without. Looks like the 717's will not have the small port but otherwise the same in function.
All of the later 261's had the lower waterpump as far as I know. All three of these and the seven 235's (all 1958-62) are low until I put Daves adapter on them.
The casting number below the distributor will be the first and most important number on the block. It would determine the features each part has. I learned all of this working at Midway Chevrolet in Moundridge, KS as a parts teenager when in High School. There may be exceptions, but for the most part if someone says they have a 717 casting, all 717's will have the same features regardless of the year or application. It would be really cool to have a list of differences in each casting for these years.
All 58-62 261's have the dowel and can be configured for either bypass or full flow. Never seen a 58-62 without the dowel.
