More parts are available for 1/2 tons because 1/2 tons were/are more plentiful.

A variety of body, brake, engine, and styling changes were made throughout the A-D years. These changes were more evolutionary than revolutionary. The 1954 year saw the largest number of substantial changes - in engine and in body style.

The 1955 Task Force trucks body-changes and V-8 engines were big changes.

Here are a few chronicles/listings of differences over the A-D years:

http://1954advance-design.com/A-D_LCVA/LCVA-1-47.html

http://1954advance-design.com/A-D_factoids/

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.