3 holes for a Swinger trunk emblem?

When you say "hood" you mean trunk lid right? If you are talking about the holes in the inside trunk frame, I think two of those line up with the two posts in the old Cursive Dodge emblem (see first picture in post 35 above) and since they were not seen, they probably didn't bother to delete them between 1970 and 1971 (when they changed to the block letter Dodge emblem (post 10).

Your hood (over the engine) should have 4 holes for the 4 post cursive Dodge emblem with provision for retainer nuts on all four posts via holes in the hood frame. One of those holes is slotted. The emblem that you buy will be flat and the first time it is installed you tighten the nuts and bend the emblem to conform to the curved hood. You always tighten the nut at the slotted hole last. It allows that pin to move a bit as you bend the emblem.