Good point - thanks for answering and the ideas - and yes, I want to co-witness. I might need to get one of those $300 Swiss Arms attachments for the stock for cheek weld etc... (too tired to remember the name) I guess as well?
If you can get the aimpoint low enough to co-witness you wont need the cheek piece. It will be a slightly looser cheek wield, but with a red-dot sight its not quite as important (you should still have a fairly solid cheek wield)
I wish I had tested my Aimpoint ML3 on my friends Black Special with B&T rail before I sold it, as it would have given me a good idea as to how close it was to co-witness. Im pretty sure the ADM wont allow for a co-witness, although it is QR so thats not a big worry.
I have heard from Green Tips posts, that the Aimpoint M4 will NOT co-witness on the Sig rifles, however I dont know what the optical centre line is.
With the ML3, it was 15mm plus half an inch, so the middle of the scope lens is about 27-28mm above the top of the picatinny rail.
With a quarter inch Aimpoint mount it would be about 21-22mm above the rail.
I don't have a measurement of how far the rear sight hole is above the picatinny rail, so I cant comment on weather it will work or not, but hopefully that will give you some idea on if you can pull it off or not.
Im pretty sure than an Aimpoint Micro would allow for a lower 3rd co-witness with the factory mount, I have heard that before... cant confirm though.
The Aimpoint Micro's centre line is about 18mm above the top of the picatinny rail.