zeogrant,

jorb and I posted just about the same information/speculation.

The only significant difference is: I doubt that the same casting number head was used on both the 235 and the 261 heads.

The 1955 261 head codes were 3703570, 3836850 (used from 1954-1957)

Can you post a link to a photo of your engine serial number? That is where we had to speculate the most. Keep posting information and people will try to interpret it.

Here is 1955 car engine serial number information.
Here is 1955 1st-series truck serial number information.
Here is 1955 2nd-series truck serial number information.

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.