It looks like there was not GM dealer option (RPO) "helper" auxiliary spring for 1949-standard ( RPOs ) or 1950-standard ( RPOs ) 3100/3600 Chevrolet truck.

There was a GM RPO heavy-duty 3100 rear spring-set in both years, but it looks like they were still a semi-elliptic set of springs.

As posted above, Dealer/Owner added non-GM auxiliary springs were available.

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.