Running without a thermostat ok?

I admit I havn't had the time to read all of this thread, I will though when I get a chance. I do highly regard a lot of opinion here! maybe this question has already been addresses.
I had a couple of old OEM radiators checked and repaired at local shop that has been in business last 40 years. ( few of these still around here)... the guy told me the OEM rad was supposed to take a 7 lb cap, not a 14. I know the boiling point of water will be higher with a 14 lb cap, and that is what I have always used., with no problem in the decades before. but it is very hard to find a good 50 year old rad now! was hard enough 20 years ago!
seems to me, if the old tank is somewhat":ify", the lower pressure cap would be a safer bet than the 14 lb cap?????