For some reasons the pictures are blocked on my computer. But, I bought a totaled Bullitt so let me tell you my experience. First off,how bad does he want to fix it? Can he picture himself driving it again? Is he one to finish what he sets his mind to? I towed my wreck to a body shop that told me I made a mistake buying it and forget about fixing it, it was a waste. My wife told me that shop was wrong and convinced me we could do it if I was determined. She was right. She stood by me for a year as I tore it down, saved our money to buy part by part and helped me find people who shared our vision and helped us put the car back together.
What are your son's skills? Does he have tools and a place to work on it? Is he willing to learn? Does he want the car fixed bad enough to drill out hundreds of sheet metal spot welds and tow the car from place to place to get the frame aligned, weld any supports if he can't weld, etc. etc? If he will always regret not trying to fix the car, then he should fix it. If the thought of working on it past midnight often doesn't appeal to him, forget it.
If he decides on the project, my advice is:
1) Get a Ford Mustang tech Manual.
2) Take the car apart piece by piece. (Don't mess with the unibody parts, leave that to a bodyshop unless you know what your doing. The tech manual will tell you what's unibody.) Take pictures as you disassemble. Tag and number all parts in ziplock bags. Don't throw out the old part until you put the new part on the car. Write wiring, fastener, left/right notes with magic marker on the old part. Helps for fitment comparison and reassembly.
3) Tag and number all wires and hoses on both sides of connections with painter's tape as you disconnect. Helps when you're re-wiring and can't remember what's what.
4) Make friends with e-bay, junkyards, ford websites, Craigslist and mustang clubs. Ask anybody and everybody for advice and offer beer for help. I asked around and checked the web and found local people with Bullitts who came over and let me look at a straight car to get measurements, check fasteners, wiring, drive train assembly, etc. They were into helping and invaluable.
5) Shop your pictures of your wreck to every body shop you can think of. Ask if they can help and or just give advice. I had two body shops who let me down, but we eventually found someone to help. We saved money by my removing all the damaged parts we could ourselves, towing the car to a body shop who straightened the unibody ($550) towed the car home, I then re-assembled the car including all the new body parts, in my garage and then got the car to a body man to paint.
6) Make friends with a mechanic who can diagnose computer stuff - diagnose/ reset airbag components, etc.
Its time consuming and not easy. There were a few times I drove through the neighborhood at night with a half finished car to get motivation, but if he wants it bad enough to persevere, it'll happen. Our bullitt's my daily driver now. I'm often driving to work smiling from ear.
Thank you for the advice!