Dave, what you might consider is building a floor framework out of angle iron (maybe 1x1x1/8) that fits the engine /trans configuration and then cut out the floor panels and fabricate new to fit the framework. The angle framework should hold the cab in the right shape.
Are you planning on keeping the original finish with the lettering on the doors? I think that would be a cool rig. Although it is kind of faded out, it would be cool to have that old lettering on the doors (maybe reproduced, if nothing else.)
