Thanks for all the info,
yes to be on the safe side and probably simpler as I understand it, almost any rim, even modern ones will fit as long they have the same ford bolt pattern. I will then look for a 15" rim for the spare and extra rims of the same size as long as I am on the lookout in case I do convert to disk brakes, which I probably will.
What I have to watch for also besode the bold pattern is that my hubcaps (originals) will still fit. In Finland there a quite a few U.S. cars, now and in the past, so I will start to visit junkyards for good rims first.