Clark Slide Mount Question

I bought this from Clark long ago and never used it.  In taking it out of the packaging now for the first time I see that the underside has a taper machined in to it but since it sits on the radius down the middle and not these machined edges, I'm wondering why it looks as it does; and why this machining was done after anodize.  It might have been for a Gold Cup - the version that has a radiused top and not the integral rib, in case this helps you figure out what I have.

I have used/ordered many Clark rails over the years. I have never seen one that had machining after anodizing. Gold Cup has rectangular groove/channel machined full length of the rail. Your rail is a mystery?
Jon

Just an educated guess.  Someone thought they needed to add the 1 degree taper to the rail.

Well I am not going to spend anymore time on this mystery.  I (now) need to buy a rail and would like to see if there is a pistolsmith in eastern Pa who can install it. I know Halston already. Are there any options in the eastern half of Pa or NJ?  I can also go the Aimpoint/Kodak route. Need to jump the line too. I have one gun. 

Machined to adapt it to a flat top 'something'?
I've never had a commercial rail in my hands, so I have no idea if they're made with 'elevation' in them to compensate for the lockup angle of the barrel. I made my own, with 30', which I derived from the irons.
If so, this is what it would look like with the elevation machined out. And I think there's enough surface area contacting the slide to not be an issue. It's just gonna look a bit weird, and drive you (me) nuts seeing it laying on the bench.

Someone machined the angle out of the rail, converting it to a zero angle rail. You will notice the rear has more material machined off than the front.
I measured a Clark rail and it has just under a 1/2 degree angle machined into it. 
Overall length = 7.125" and side opposite is roughly + .060" = just under 1/2 degree.
An Al Marvel rail is about the same = Just under 1/2 degree.

Yea but you are measuring the radii.  This machining has nothing to do with the position on the slide.  It’s aesthetic. They machined the taper in a non-functioning feature. And, they machined it in the wrong direction. Even IF the rail used this surface to position itself, the rail would be angled UP.  Is marijuana legal where Clark is? 
I like that you have your name engraved on your calipers.

If I was measuring the radii, I would be using a radius gauge. 
I am measuring the difference on each end of the rail to establish the side opposite dimension = .060" difference. This allows me to trig out the angle relative to the scope mounting surface = just under 1/2 degree.
The person that machined the aforementioned slide rail mounted it, scope side down, on parallels in a vise and ran a radius cutter down the length which makes the top and bottom parallel as shown due to more material removed from the rear of the rail compared to the front.

IF it matches existing holes in your slide, put it on and play with it. Assuming you have it already drilled.

I wouldn't driill a slide for an odd duck though. The hole spacing may be standard but I wouldn't bet on it.

Ahhhhh.  The clouds have lifted. Thanks Wes. The anodize having been removed drew all our attention to that surface.  I’m so embarrassed.