"I guess my question is, did the smaller trucks (pickups and such) not need the bypass feature on the 261?"
The 261 was not available as an option on smaller trucks.
You can safely use the 261 without that feature. The 261 allowed the by-pass feature, but the use of that feature was not required .
That feature not used on either of my 261 engines (1959 & 1960). One engine was originally used in a school bus. One engine was originally used in a high school truck-shop class (never used in a truck). On both engines, the holes were plugged on the 261 thermostat housings and on the matching 261 water pumps.
Both engines are now in 1954 3100 trucks - one for over 10 years and one for a few decades.
Both engines have Dave's adapter plate and 1954 235 water pump, and 1954 235 engine thermostat housing (with a 1/8" hole drilled in the thermostat).
