Tracking Build My Gallows High

 MV Features' Western Star Picture Library #5 was published c.1965:

I'm betting the story Build My Gallows High is the one reprinted by Page Publications in Gunfighter Library #2:

And in Badman Western Library #5:

And in Six-Shooter Western #5:

The top two covers are by Keith Chatto, and the third is from interior art:

The MV Features reprints by Page Publications often include an abbreviated series title and issue number native to the original prints but these reprints do not, so it's an educated guess regarding the source material. And since I'm in guessing mode, I'll also assume there is an earlier edition of this story with a Chatto cover based on the cover of Western Star Picture Library #5; that there is at least one more edition of this story published by Page Publications; and that Six-Shooter Western #5 is the last edition published. TBC.

For identification purposes, here's a scan of the splash page to Build My Gallows High as it appears in my copy of Badman Western Library #5:

It's not my cleanest copy of this story, but the Gabba Book Exchange stamp makes it better.

Update 23/9/2022: This story also appears in Blazing Western Stories #3 under a Chatto cover:

Update 17 July 2023: This issue was also recycled as Six-Shooter Western #4 under a Chatto cover: