I am putting a 56 GMC body on a 69 C10 Chassis.
The 69 is one inch longer than the original chassis

I purchased a almost "Rust Free" bare cab on Ebay form a guy in Mesa Arizona

We had to add about 2 1/2 inches to the end of the frame for proper bed placement.
Using the pre drilled Bed Wood for alignment of the cross braces.
Looks like the fuel tank will need to be lowered about an inch or two also.

   
     
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Click on the picture for full size image.
Scott (AKA: Cadman) smumfor@yahoo.com