fisrtly, where the heck did you find a pretty rust free truck in BC?
secondly, nice work. have you decided on what to do with the frame yet? it may come down to what you wanna use for power as well, what the frame you choose can handle, what it will have for brakes, axle, etc.
there is a thread on here that shows a fella who put a '58 panel on top of a gmc envoy or chevy trailblazer frame (actually, a saab frame) and some of the body was used I think. there are a couple of other builds using the chevy trailblazer or gmc envoy as a donor as well. maybe it takes away some of the value of the finished unit, compared to an original frame, but if you modify the original frame then, for me, it is 6 of one and a half dozen of the other.
http://67-72chevytrucks.com/vboard/s...d.php?t=823156
another on a trailblazer but not a panel truck
http://67-72chevytrucks.com/vboard/s...d.php?t=517183
if you google
55-59 chevy truck factory asembly manual
and pick the trifive site, the assembly manual is a free download. I suggest doing that and downloading to a thumb drive so you have access to where all the spot welds are, how things were assembled at the factory and, more importantly for you and a frame dilemma, it has frame dimensional drawings.