Installing a 54 GM bed on a 47-53 Frame: Some options, none easy

We often are asked about the possibility of installing a 54-55 GM bed on the earlier 47-53 chassis.  Some callers may prefer the appearance of the later bed or others may have access to one and wish to install it on their 47-53 frame. At first this looks like a simple conversion as the shape of the frame and the mounting bolt patterns are similar for the two trucks.   A close look at the two frames will show the critical differences that make the conversion difficult.

The main problem with installing a later bed on the 47-53 frame is the earlier frame has a much higher "kick up" or arch over the rear axle area. It is about 4 inches higher than the rest of the frame and the 54 frame "kick up" only rises about 2 inches. A 47-53 bed is installed on wooden blocks under the cross sills that raise the bed about 2-1/8 inches so the bottom of the wood is about 4 inches above the frame, which allows for the 4 inch kick up over the axle.  The 54 bed does not use wood blocks under the cross sills so the bottom of the bed wood floor on a 54 truck is about 2-1/8 inches above the frame.  The photos show the two frames and the profile of the 54 frame is noticeably flatter than that of the 47-53 frame.

The result of all this math is that when installing the 54 bed on the earlier frame, the bedwood boards rest on the frame kick-up and the cross sills will not rest on the frame as they should. This effectively raises the bed about two inches above the desired installation height and there just is not a simple way to lower the bed to the right position without major surgery on either the frame or the bedwood.

If you attempt to install wood blocks under the cross sills to mount the 54 bed, there are several areas that will still be a problem. The 54 splash aprons above the running boards will not fit, and will not fill the space between the running boards and the bedsides. Also, the fenders are attached to the bedsides, so they will also be about 2 inches higher than they should be and like the splash aprons, will not connect to the running boards.  If the fenders are lowered on the bedsides, there are all the fender mounting holes to weld up and relocate on the bedsides.  Fender braces will also have to be modified.

Another option is to modify the bed wood and bedsides by raising the wood floor relative to the bedsides approximately 2-1/8 inches. This can be accomplished by moving and re-welding the angle strips up 2-1/8 inches on the bedsides so the bedsides and fenders will therefore be mounted in a position that is similar to the original 54 location.  The cross sills will need to be raised to support the wood floor, so some spacers under the cross sills such as wood blocks will be required.  Also the rear sill will be 2-1/8 inches below the wood and a spacer will be needed there to fill the gap.  The 54 front panel mounts to the bed wood so a 2-1/8 spacer will be needed there also.  Aside from the difficulty of making all these changes, a problem with this option is the end of the bed wood that shows above the rear sill when the tailgate is opened. 

A third choice that builders who are confident in their welding skills may prefer is to modify the 47-53 frame to more closely match the shape of the 54 frame. The top of the frame is chopped down about 2-1/8 inches in the area over the rear axle and is reinforced to compensate for the metal removed.  The complete 54 bed could then be mounted on the earlier frame similar to its original location and the bed wood floor could be installed like the original 54 bed.  The 54 front bed to frame mounting hole is about 3/4 inches different than the 47-53 bed, which requires drilling the frame for the new bolt location. 

If you are using a 47-54 frame from one of the custom frame fabricators, be sure that it is designed to accept the bed that you plan to install.   If the axle kick up over the rear axle is more than 2-1/8 inches, the 54 bed will not fit without modifications.   Make your measurements before committing to the rolling chassis and avoid an expensive mistake.

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