I think the OP is correct because he stated NRA matches were his interest. Near as I can tell, optics ARE permitted on M14/M1A service rifles for NRA only, if you can meet the 3.5" over bore requirement.
Quote from rule book in the service rifle section 3.1
"The rifle may have an optical sight (reflective sights are considered optical
sights) with a maximum of 4.5X are permitted. Only commercially manufactured
scopes that were produced with a maximum magnification of 4.5X
and that have a maximum objective lens of 34mm may be used. If an optical
sight is used, the same optical sight must be used in all stages of a course of
fire (changing sights is not permitted). The centerline of an optical sighr shall
be no higher than 3.5 inches above the centerline of the bore."
Section 3.1.c (specific to M1A/M14)
"U.S. Rifle, Caliber 7.62 mm M-14––Must be no more than 2 inches
wide at a point immediately to the rear of the front band, no more
than 2 1/2 inches wide at the front and rear of the receiver, and have
a continuous taper from receiver to front band. Width at receiver
may be carried through to the butt plate, which may be the flat M-1
or hinged M-14 plate, which will be used only in the folded position.
In all courses and in all positions the standard 10- or 20-round
box magazine or a reduced capacity magazine of the same external
dimensions will be allowed. For stock dimensions see diagram."
And of course if you want to step out of the Service Rifle category and into the "match" rifle.....then all bets are off.
That aside, scoping the 14 for service rifle class but being limited to the geometry of a standard stock, may not work as well as you would hope due to the elevation of the scope above the bore.
