Anschutz makes several different actions.
Previously, the Model 54 was their top of the line and the 64 was the lighter, less expensive model. (There have been model # changes and new variants brought out since, but those actions still form the basis of much of the production.)
The 54.18 MS (and the 54.18MSR -- the repeater version of the 54.18 MS) is based on the higher dollar 54 action and it is a more costly rifle with a much more sophisticated trigger (5018), better bbl(?) and more finely-done finish than the rifle based on the 64 action.
If you're familiar with older Winchester production, think of the 54.18 as the M52 Target and the 64 as the M75...the parallel is pretty close.
