That is fairly tricky, isn't it
For best appearance, I think I would mill the part with the legs facing up first. I would use a piece of stock that is high enough that I could grip a sacrificial sliver along the bottom (say 1/8 to 3/16 thickness) in the vise. Mill all the features that you can in this initial setup. I assume you are using some sort of chamfer mill to mill the sloped dovetails. This will give you completely finished faces where they bulge out in arc form, instead of trying to match those up by machining halfway and then flipping.
Then, machine a spacer for the part. This spacer should be of such dimensions that it is a close fit in the groove through the part, and has a small circular boss on top to engage the round hole that you have already milled in the part.
If you are in mass production mode, you should be able to make this spacer long enough to contain 3 or 4 circular bosses, so that you can mount 3 or 4 parts for the secondary operation.
Of course, this spacer is a precision part, and you will need to have one of its ends faced to serve as a datum against an end stop on the vise jaw.
Set the half finished pieces up so they straddle the spacer and engage the boss. Then clamp the part in the vise across the flats of the legs. The spacer then serves the purpose of preventing the part from collapsing from the pressure of the vise.
Use a dial indicator in the spindle to sweep the holes where the engage the boss on the spacer. This assures a correct initial setup. In your CAM, create a new program assuming the part position is centered with the XY datum on the hole.
Facemill the top of all the parts, removing the sacrificial material, and then finish the counterbore in the part, above the locating boss. Mill the chamfer dovetail as the final op.