The swap to 126 and 6-speed was well before SunTour started making the Ultras in any form. I think the first 6-speeds were well before 1974 though I will not swear to that. I do know that the Ultra spacing started (in this country anyway) in 1978, maybe 1977 though the top end Fuji Professional with its sweet SunTour Suberbe was a 126 6-speed and had all the top SunTour stuff that was not available anywhere else until the next year. (Fuji and SunTour having a very close connection.) The word 7-speed was never mentioned. (I worked at LifeCycle in Cambridge, MA, the dealer for Fuji for the northeast.)
6-speeds before the Ultra spacing and 7-speeds after had exactly the same issues (dish and axle breakage) as the dropout spacing and hubs were identical. It became apparent very quickly that going a step further to 8-speed and 130 was completely out of hand and that (didn't start but) quickly drove the move to cassettes; allowing the outboard hub bearing.
Ben