57Rat, I love the reason you put for editing your post. LOL! If you have any other ?s about your truck feel free to PM me. I have a 59 GMC. My first truck ever was another 59 gmc with a 270 6 cylinder and a 3 on the tree. All in all I have had 3 '59 GMCs, 1 '57, and 1 '1940 GMC. There is another forumn that has more GMC specific information.
For the most part the chebby and gmc sheetmetal, beds, and fenders will interchange on the 58-59 models. This is not the case for the 55-57 models. GMC ran different motors than Chebby. The GMC 6 is about 1-2 inches longer than the chebby 6. This brings about a condition known as "long motor envy". The GMCs were the choice for work trucks, and always offered a little bit more than the chebby for the same money. GMCs are more rare than chebby and consequently GMC specific parts tend to fetch more money than the chebby specific parts. There are other differences such as grills, and dashboards which are eazy to spot.