What all is interchangeable ?'s

[low&slow]

Hey all. I'm sure this has been brought up a million times, but it never hurts to bring the topic back for an update in the search thingy.

Just picked up a 71 gmc 1 ton dually in perfect condition. I have no plans for it other than take a few parts off it for my other builds. Questions are below and will be numbered. Please state which number you are answering too. Thanks

1. I have a 68 chevy 1 ton and I need a driver door. Will the driver door off the 71 gmc work? If I change the door do I need to change the passenger door as well?

2. I have a 67 c10 and the fenders are rusted out on the bottom front. Can I put the 71 gmc fenders on, fill in the marker light, and still have 67 fenders or is there a difference in the fenders?

3. The 71 gmc has metal door panels, will they fit on a 69 chevy door?

4. Can I take the rear end out of the gmc, gut the housing, and put shorter axles in to then have a narrowed rear end for my c10?

5. Is the front bumper on the gmc the same as a front bumper for a 72 chevy?

Thanks in advance.