As usual, Pettifogger gives good advice!
There's another issue to this, but it isn't nearly as important as the reliability issue. The "improved" models are shaped differently - I'm talking about the dished out part. I had the rare privilege a few months ago of handling about a half-dozen original '66s ... and one Henry. ALL (the '66s ... NOT the Henry, of course) had a more triangular "dished-out" shape than Uberti used to put on their rifles. Now, they were all 1st, 2nd, & 3rd models that I saw - I don't think the owner had any 4th models there ... which is what Uberti copied. The replacement gates from "Track - Wolf" were all like the originals, NOT like what came on MY rifle. It's a cosmetic thing, but if you re-enforce one of the new ones, it will both perform well and look authentic.
I can't (couldn't) tell if the originals were case-hardened or not ... too much time and the colours tend to wear off much quicker than bluing, but it's my understanding that the colour-case-hardened gates would also be the most authentic looking. "Back in the day" I think that the loading gate & lever, and the hammer & trigger were all case-hardened. (I'm talking about the dished type, not the flat ones on the first models.)