Early IOR quirks
The "IOR" syndrome, is a reflection on the design results of trying to get the best performance under the racing rules of the day.
The end results were boats that had smallish mains, what were called "High Aspect" mainsails, and gigantic (in proportion) foretriangles.
Hull forms favored by the IOR rules had "Pinched" ends, especially the transom. The major flaw in the designs were a propensity to broaching. The boats would begin to heel, the rudder would become uncovered, the helm would lose bite and "Viola" a broach. This was most evident running, with the giant ''chutes up and a following sea. A helmsman needed eyes in the back of his head to watch the waves both in front and behind.
These designs also favored big muscular crew, to handle the enormous headsails, and the constant "gear changes" necessitated by driving a boat with the genoa and not the main.
Some designs were worse than others, and some even worked well, given the rules.
You can take one of these older designs and tame it, yet it will usually always be a compromise. Change the 170 - 165% genoa for a 130% and put a main on that has a larger roach. You will go slower, and not be as well balanced, but it will be less work. Also keep the spinniker in its bag on windy days with a following sea.
IMHO I always liked the look of the boats from that era, that''s why I have a ''76 One Tonner. But I also chose mine knowing the ones that worked, vs. the ones that didn''t. And I also respect the challenge that sailing her entails.