May I suggest asking the following line of questions?
1. Is there any personal connection/history with the vehicle that would cause you to keep the car "no matter what" when you are done?
2. Do you want to break even for real dollars spent and make at least $10/hr (put your own figure in there) for the time you put in?
The first thing to consider is the cost of a concours restoration, both in dollar outlay and hours. For example, the final cost of reworking an Acapulco Blue 68 J code 4-speed fastback in similar condition would cost virtually the same as the car you discussed. How much more would it sell for when done? Moving "up" to a 428 CJ would cost a few percent more to restore, but all things considered still not significantly more. The entry point (initial vehicle cost) would be more, true, but the restoration not much more. Yes, you will find the need for a $500 starter relay rather than a $50 one, along with some pricey ram air stuff, but the bulk of the work; sheet metal, suspension, interiors, paint, and yes cleaning up all of the fasteners is pretty much the same cost whether it is a 6 cylinder or a big block. So if you do the math, if a basic vehicle restoration will cost 100%, a big block might be 10% more, a Shelby 20% more. Some might argue the exact percentages, but it is not +50 or +100%. Add to that the initial cost of the vehicle, and you have a total cost. Then look at the value when you are done.
Of course, it gets complicated when you toss in some passion. My first car, like my first car, in the family X years/generations, a Marty 1 of 1, and the like, fuel that passion. I suppose that with no passion at all, it would be like a second job. You generally will look to make some money on a second job. The challenge, as you mentioned, is another thing that falls on the side of passion.
As you stated, the car is a V8, it has some nice options. Your favorite color. A "challenge" to look forward to. However, the reality might be that you don't make any return on the hours you put into it. That's exactly where I am with my project, and I would not have it any other way
Good luck on the decision!