On some norc and springfield receivers I have found the mount groove (just above stock line) to be a bit tight for some mounts. this can be adjusted carefully using emery cloth, essentially deburring the edges of the groove.
I have also found the flat area around the scope mounting hole to also not be totally flat on some norc and springfield receivers and again, emery cloth on a piece of small flat bar or similar and polish this flat, paying particular attention to the edges.
I personally feel the arms 18 is the easiest mount by far for mounting to the M14 but the smith is nice also. The arms 18 can be tricky for some as well, but there is a procedure that must be followed on rifles that it does not readily mate to.
I NEVER, not EVER have had to shim or remove major material from mount or receiver to accomodate the arms 18 and smith mounts. a light polishing and deburring yes
along with having levels on hand, a good trick is to have a 3/4" dowel or round stock steel about 18 inches long to use as a reference guide once the mount is on the rifle but not yet tightened down. with the arms 18 center groove it makes it easy, just lay the dowel in the groove and you will see immediatley if the mount is not in line with the barrel.
there are times when the instructions with a mount only help so much as they do not account for minor variances that can cause major affect on POI down range.
some good advice in this thread.... keep it comin
