Duane,

You have not shown the GD&T callouts on the sketch. Fig. 1 could be used to inspect the slot RFS to A|B (there is no need for -C- here). Fig. 2 could be used to inspect the slot with MMC as far as it does not violate the virtual condition boundary. Note that when the slot departs from MMC it does not need to remain parallel.

If you are trying to establish A|B|C you would align as in Fig.1. Fig.2 can be used for A|B|CM (C with MMC modifier). When MMC is used you normally have an infinite number of datum reference frames that can be used and if you can find at least one that works the part is good.

George K.
Sitius