Value of Stock vs. Modified to Increase Driveability

So I'm starting to help my brother with his project which is a 68 Barracuda convertible 318 2bbl, orange with a white top and white interior. It's rough in places (no trunk floor and needs quarters), and we've been talking about how modifications effect the value. For example, it has 10 inch drums all the way around and an 8 3/4 323 sure grip. I have a Kelsey Hayes disk setup and the correct sway bar for it, but I wonder how that would affect the value of the car as opposed to 11.75" rotors and big bolt pattern. I thought I'd put small bolt rallys on it, which are also in stock, but raised white letter BFG's are $600 a set, which blew me away. It makes me wonder if the stock look is really the way to go, versus a more powerful, better stopping, and possibly better looking version of the car. It has the original motor and trans, which hasn't been run since 1980.
At any rate, I'd appreciate any feedback about your take on the value of stock, not particularly rare and good looking vs. not so stock and much more fun and safe to drive. Appreciate it guys....
Assuming that the car is not intended to be a short term flip, I believe that a car should be built as the owner wants it and can afford to do so. When choices are made to impact the ‘cars value’ unless the car is a rare collectable car, it is usually a losing proposition.