I seen that and the problem with dimension “B” is that this is the max sectional dimension, the dimension actually varies the length of the frame. For example I measured the rear of my frame and it measure 2.405”, I measured near where the rear motor mount is and it measures 2.75”, and I also measure the front which measures 2.36”. GM also changed their part number for the frame in 1954 as there was a change to the rear motor mount. So even though dimension “B” is the same for the 51 and 54 frame, the actual dimension where the motor mount sits could actually be different. Before I start removing material, I want to ensure that my measurements are correct.

Thanks
Dave

1966 Chevrolet Caprice 2 Door Hardtop (396 Big Block)
1951 GMC 9434 5 Window (waiting on a 292 transplant)