Well... from where i am, that car can, should and would be repaired without thinking it twice but if it is so busted, then you can think of alternatives that can lead you to a safest end...
I dont know much about what mach1 code is better than other but forgetting that, if you have a car mostly complete with a good factory option combo and what´s bad is the shell, then use it, but with another shell...
Luchy we are, in our era mustangs, all shells are identical so you always can purchase a good sportsroof (they are tended to value more each day but if your shell is destroyed, then a 7, 8K sportsroof is going to be cheaper than fixing yours anyway) and start from there... using the most solid shell, accident free you can get and thinking you´re restoring the mach1 with a donnor body...
First of all, if i were you, i´ll check twice about the vin you´ve red is positive, the car vin... I notice the passengers door appears to be changed, so can be the drivers door where the door tag is... Also, ive seen in Ebay, some fellas that sells the upper instrument panel metal sheet (the one that has the other visible vin) and they sell this part with a mach 1 VIN on it...
Scott knows better than i do, but there´s another sport in the cowl where the vin is stamped actually in the body, making it very difficult to change... I think it is readable from the inside better than from the engine bay and it is located behind the heater, in the center of the fron cowl, just above the transmission tunnel...
Well... hope it helps someway!