While this isn't a Howe-Whelen sight, it is mounted on a modified 1903 bolt shroud and retains the
safety. The adjustments are crude and similar to some of the Lyman sights like used on the Savage 1920 and some Mannlichers.
One good thing about it, is that the rear aperture can sit quite low. The front sight on the rifle it is on, is only about 0.9 inches above the centerline of the bore, [Linked Image from i.imgur.com]

It does have the little detent that Howe suggests in his book, to remove the play in the bolt shroud.

[Linked Image from i.imgur.com]

Regarding that Howe-Whelen sight that sold on gunbroker, the seller has another complete 1903 bolt, complete with a Lyman
cocking piece sight, I can't see any evidence of a detent though.

1903 bolt with cocking piece sight