Carl has a good point about avoiding messing with the powder coating on the frame. If you move the hole in the cab to match the frame, you can deal with that as far as avoiding rust, but you'll have to deal with the depression in the floor unless it's just a hair off.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.