I had a Dodge W20 with an NP435 (granny gear manual similar to the 465) with a non-working parking brake. Once I pulled up in the edge of my yard to run inside real quick with the engine running and the trans in neutral. I thought I was on flat ground, but when I came back out, my truck was no where to be found. It had rolled across the street and was up against a fence about 50 yards away. No telling how far it would have rolled if not for that fence.
I really like your build so far man. I still just can't get over how good your bench seat looks. If mine had looked that good and hadn't been sprung and worn out, I probably wouldn't have swapped to buckets.