mosin PE mount base with cantilever possibility

[rabies]

i have found this in my search for a good mount.

its the base of a PE sniper scope mount.
i hear you can not mount standard weaver or dovetail rings on it.
i havent bought it yet. can some1 plz tell me why the standard rings people use dont fit?
is it because its between 11mm and 20mm?
is it because there is no sideways notch for the set screw?(easy fix)
can someone that has one measure the width of the rail on the top?
in the end id like to use a cantilever mount and nikon monarch scope with it.
anyhelp is aprecaited. i dont really want to go in any other direction.
iv tried a few mounts. i wont be drilling and tapping. only welding since its steel and if its jus right il leave it permanent

[rabies]

it came in the mail.
heres the result. it clamps down. but i bet it will slide off. and its a tad cockeyed.
the clamp screws sit ontop the rail. if there was a groove for them they would keep from moving. but theres not enough room for 2 rings though. the middle fo teh scope is too big. but you could use a cantilever.
il only post this for future searchign by others with curious minds.