After seeing some additional pictures, I will repeat my advice from above - - "Other than a good detailing, I wouldn’t put any more money into it, as it won’t seriously effect its sale price in the market. Actually most serious buyers would rather fix whatever they want, the way they want. They would rather see it “as is” than worry about “cover-ups”, or “cheap fixes”. (not saying you would do any of that - just pointing out the skepticism in any used car market)."
Looking at the additional pictures - - I'll add, messing with such an original condition 240Z - can actually reduce its value to the most serious collectors. They will not only have to address its minor flaws, they will first have to pay their professional restorers to undo what ever you have done. They will pay more for a car that hasn't been messed with..
If you want to help your Dad get the highest dollar value, I would say spend your time and money getting clear high resolution pictures of every detail. Get that Z up on a lift and get pictures of the undercarriage, lots of pictures of the most common rust areas. Take the battery out and get clear pictures of the area under the battery. Pay a professional photographer to provide good high resolution well lite images if you have to, pay someone to put the car up on a lift so you can get great pictures. IMHO that would be the best time and money you could spend on the Z.
Go look at the Series I 240Z that sell on BAT - read the comments - you will see that the cars that sell for the most have a couple things in common - 1) 150 to 200 great pictures and 2) a seller that stays on top of answering questions and responding to requests. To get the most value out of a 50 year old Classic Car - you have to put the most effort into SELLING IT.
Good luck,
Carl B.