I've viewed this car, there is less rust on the Titanic. Most major original engine components are missing and replaced with aftermarket including the Distributor, Carb, Inlet Manifold and Boss 351 only Crank dampener which could mean the original Boss engine has been substituted with an ordinary 351C. Shock towers and doors are rotted out so guess what the cowl and torque boxes are like!...
Exactly what I was running into when I was looking for a 71 Boss on the cheap and ended up buying a 71 M Code Mach1. I'm now back looking for a 71 Boss but far more educated; my primary requirement is unmolested, with original drive train that's not a rust bucket at a reasonable price. I don't see the value a car like that going any where but up. I would pass on the one as described.
Good luck... I can tick off two of the three requirements you note above, when I purchased my '71 429 cj convertible this past June. The "reasonable price" I seem to have forgotten when I agreed to the deal at the time.
As I go through my restoration now, I realize that the purchase + the restoration costs will surely out distance the eventual value of the car... However, I am still glad I bought it and I know I will enjoy for years to come and when I do go to sell, should still bring a decent $$. The moral of my story, sometimes you have to spend to get what you want at the time. Cheers.