To start with, the entire run was not called second series. There were 2 series of trucks in 1955. The second series was the first of the Task Force Chevrolets and the Blue Chip GMCs.
In US models Chevrolet and GMC frames are different. Canadian GMC trucks used Chevy engines so those may be the same. Also, '55-'57 frames differ slightly in length from '58-'59 frames.
Long bed frames are longer than short bed frames.
