Yes, there were several changes in metallurgy.
Yes, IMO the Winders can be case-colored with no problems, as can all the original walls. FWIW one of my smithng mentors built a Winder low wall in Hornet 60 years ago, it's still case-colored and his son is still shooting it. Gunsmith Jerry Kelley of Nebraska has been building BPCRS rifles on Winder low walls for many years and several of them are case-colored.
These Winder low walls have the flared sides of the earlier low wall receivers while at the same time having the large thread shank and thick lower tang of the high walls. Thus it's easy to fit orphan tangs, triggers and barrels from high walls, giving more versatility, and the round unscalloped receiver ring is, IMO, much more attractive. The coil-spring-action lever tension spring is a PITA during reassembly and I personally don't prefer or even use it but otherwise the late coil-spring actions are splendid.
Regards, Joe
