[davepl]

From my cursory look at the Blazer section of the assembly manual it looks like they just cut down full cab trucks, so you could certainly look to it for guidance (but finishing out the top rail I don't know about).

I have no idea how much the rigidity of the cab is important to these trucks. Usually if you cut the top off something that wasn't intended to be topless it's a disaster. To what extent the existence of the Blazer variant helps I don't know.

I wouldn't cut that truck you posted though. Unless it's a 20-footer it looks far too nice to start chopping up. At least buy a rusty practice truck first!