Not only is the right, automotive epoxy clear harder, and more clear, the most important factor is finish materials were/are not made to sit 30-40 years then have the friction of a heavy ball rolled over them. AS with any finish, it may still look new, but at its age it is brittle, and will wear very fast. Even if it did not, since you are going to remove all of the parts and do an enormous amount of work, this is the time to make it perfect, and insure that it will last longer. I dont habve the time to write the book about the advantages of properly clearing a nos pf from the late 70's, but just imagine installing a nos prepainted body part that has been sitting in a garage corner, on to your newly restored 66' barracuda, without at least sanding and reclearing.
Lastly, and this is going to make a lot of people mad, but water based varathane, looks just horrible, and is not nearly hard enough. Of course this is the opinion of someone who clearcoats pf's for a living. (the ones that are used on restoration projects that sell for 12-15k) snob.
Also the right auto epoxy clear works great on pf's when done properly. Experience is very important. Naturaly the first one you do is not nearly as good as the 500th. There are a lot of tricks that dont show, but make the job look and last better and longer.