MSTN has this great topic on mounting a scope on an AR MSTN scope mounting.

My question is between the MOD 0 (with a full length PRI rail) and the MOD 1 with the flattop.  
Does using the Larue scope mount make sense on the PRI rail or does it raise the scope too high? or is another mount preferred?

The LaRue Mount put the optic at 1.5" centerline.  If mounted on the SPR rail of the MOD 0 add another .365".  That would be a tad bit high.  The Larue mount was more or less designed (IMO) to cantilever the optic (similar to the ARMS #35) over the foreend to adjust for proper eye relief.

MOD 0 use the ARMS #22 Medium Rings
MOD 1 use the ARMS #35 Track Mount and Medium Inserts.  The LaRue mount is an excellent alternative.

Since the introduction of the leupold MR/T scopes, with shorter eye relief, the MOD 1 and SAM-R (East Coast) can use ARMS #22 High Rings or similar, since proper mounting for eye relief can be done on the receiver itself.