I just bought this today and finished installing mine.
Very solid mounting within the existing rear iron sight mount.
The front of the rail block is a precise match to the front pin.
The rear Allen bolt threads into a bolt that, for lack of better terminology dove-tails into the interior slot of the sight block attached to the barrel once the rear sight spring is removed.
There is a further seat that mates up with the top of the rifles receiver.
I too was concerned about the positioning of the rail as it looked like it would set a regular scope too far forward, making the shooter crowd the rear of the bolt to allow proper eye relief.
I test fitted a couple of existing spare scopes I have on hand - a Vortex PST 2.5x10 and a Nightforce 2.5-10 NXS - both of which work just fine.
As with most mounts that are retro-fits, this thing sits quite high.
So now I just need some ultra-low mounts and and a cheek pad - otherwise it turns into a chin weld.