Adjustable Rear sight

Who's adjustable rear will drift in to a mil spec dovetail and work correctly as was done on older hardball guns?

I would a call to Kensight near the top of my list.

+1

Kensight you will have to drill and tap the slide for the elevation screw.

It doesn't cost much to call and check.
The product line may have been changed, but my ball gun has a Kensight that does not require drilling & tapping.
If you're married to a lower profile assembly you will have to  drill & tap for the elevation screw.

No go with either Kensight or Fusion.

LPA has a.small adjustable.rear.sight for the std. Governemt cut

I'm going t keep an eye out for an old Bomar type BMX which is the exact model I'm talking about.  I just learned this thanks to my old copy of Gil Hebard Guns.

Will the front sight be the right height for a new rear sight?

I put a Kensight no drill on my colt series 70 government 45 year old and had to by tallest front sight I could find and it was to short but a welder fixed that.

Richard

Is there any reason, if I have my gun built with the more popular 3/8 x 60 deg dovetail, that I couldn't just mill in this feature alone without the additional machining to bury it, and drift in any sight with this style male dovetail?  I just thought of this and also notice that I did not give enough information in my OP; the gun is a ground-up build so right now the slide is totally bald.

A pertinent piece of data!!!!  You can do what ever makes your heart skip in that case.
You just have to make sure the front and rear sights are in the correct relationship to each other (just measure the heights of a gun that works for you & mathematize backwards).