Nothing magical about IPs. Beyond a scan of the original negatives (they’re not separations), that would be a perfectly acceptable source, presuming created properly.
Among some other very interesting titles, Kino Lorber is releasing two early three-strip Technicolor productions, Doctor Cyclops (1940) and Cobra Woman (1943, released in '44.)
We've not had great luck with the quality of Universal / Paramount Technicolor of late, and I was very pleasantly...