I think we will reassemble it for sale, and the "look" will be that we want it to be as authentic as I can make it without getting into concours territory. It's up in the air, honestly.
And do you mean the area indicated by the green arrow was painted black at the factory?
That are from the radiator support to the firewall surface was typically for most of the year a mix of three colors/paints. The body color from painting the body (visible sections after assembly) the base red oxide epoxy primer that would match the bottom of the front frame rails - firewall forward and black from the painter who painted the engine compartment and radiator support. On rarely found examples you can find a painter who applied body color all the way forward but he was wasting time and product/paint/$$$$s so the body color often extended forward to the shock tower insert area. The guy who painted the engine compartment black would have applied paint to the top lip of the engine compartment and the radiator support which would have produced overspray (last paint step) on to the lower and those directly behind the radiator support panels in the wheel well. Often, he would extend the black rearward to or short of the front edge of the shock tower insert. Any or all of these general stopping points could move forward or rearward depending on the day, worker and other reasons. As mentioned there are extremes but if you haven't documented them on the specific car your building would suggest that you don't reproduce those patterns but stick with what was typically done. Have plenty of pictures of this area from unrestored cars if that would help
To help with that we would need to know when the car was build at Dearborn. This date is available from Kevin Marti in one of his reports. Projected/guess upon date from the door tag, build sheet or other places on the car will not help.
Understand that your not going "concours" but you have to refinish that area anyway so might as well try to replicate the factory finish since you will not be coming back to correct it later, if you change your mind. Other items that bolt on an off can be corrected with a lot more ease if you change you mind later or choose to sell the car. But if your doing an all out modified or altered car anything goes
Good luck with your choices
The following are not specific for you cars production period but wanted to post some examples that shows some of the three color combinations I often find
NOTE to others readingn this. different factories had different practices so the above information is not meant for 65-67 or 68 Shelbys
Hope this helps