How much picitiny rail do to need to attach the m4/s reliably?  I'd like to put this optic on a LRB M25 m14.  The rail on the m25 is 4 1/2 inches long.  The front and rear part of the rail that you actually mount to is 1 inch.  Is this enough rail to attach to, or should I get a comp m3 so I can use 1 30mm ring?  I'm hoping the m4s will attach to my rifle with no problems.

Here is a pic to help out.  the light yellow line is 4.5 inches.  the red line is 1 inch. will I have a hard time mounting the m4s on this rail?

With what you show, I would go with the M3 and the 30mm mount.  The M4 has a center groove that really does not hold anything.  Need more rail for a M4 to work.

what about putting the m4/s up front, like a scout set-up?

No go on the scout setup.  I go the M25 receiver for a reason.  Thanks though.