There is no "answer" for the question directly. How "vintage" do you want to keep it? Do you want a rig which looks like it came out of a time warp, or a museum? Nothing wrong with that at all, but if so, probably a '58 should not have an AC on the top.
If you are doing a full renovation with all new interior, and so on, why not go with modern stuff, including a good AC unit.
A few have tried to build an AC unit inside or underside, which does not show, yet cools. Kind of expensive and difficult as it would be a custom unit, but possibly another option.
Where do you live? How do you travel? If you live in a hot, humid climate, most want AC today. If you boondock a lot, your only power would be a generator, and you might not want to bother. If you always have power available, as in commercial campgrounds, and live in a hot climate, go with an AC unit.
In my own case, my '71 Caravel
has no AC, is almost totally original (although AC was available in '71, mine did not have it) and I boondock mostly, so no power is available. I would not add AC to that rig. But my '74 Argosy is so far removed from original I feel no pangs at all about changing it in any way that makes me comfortable. It came with an AC unit, which is mostly unused, but there if I want to take a trip into hot country, where I will have hookups.
So, no answers from me, only things to consider about your own feelings and uses of your rig.