It would be interesting to know if Clint has ever said anything about it
It's clear that High Plains Drifter isn't by any means a remake, but it seems possible, maybe even likely, that it was inspired by Django il Bastardo
I don't know if Weisser or Bruckner talk about it, but Mario Giusti does mention High Plains Drifter, but he literally says that "the film (Django il bastardo that is) is often mentioned as a source of inspiration for Clint Eastwood's masterpiece" In other words, he doesn't refer to any specific article of interview.
The land of bull ... who knows
It's also often said that Eastwood considered for some time a remake of THE GREAT SILENCE
Watching this movie, I had the idea it influenced at least UNFORGIVEN, JOE KIDD and PALE RIDER (and maybe even HANG 'M HIGH, there is a barroom scene with Clint throwing a match that looks very similar to a scene in TGS, but it's hard to imagine that Clint saw TGS before making H'MH)
Watching KEOMA last week, I noticed that PALE RIDER was influenced by that movie too (visually)