The cross member under the rear of the engine changed in 1954. This allowed the elimination of the cross member and support at the rear of the manual transmissions.
http://www.1954advance-design.com/Documents/EngineeringFeatures/slides/Page49.html

Special cross members in those two locations were needed/used on trucks equipped with the heavy Hydra-Matic transmission.

The 1954 3100 rear end is a 3.90 ratio. A 3.55 R&P swap is possible in that enclosed driveshaft rear end. Check the Tech Tips on this site.

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.