Nikki - I'm in the same position as you (there is one other word that would fit for 7 down, but that would be even weirder than the one you've deduced if we're looking for themed clues).
I'm wondering if there is some poem, or passage in literature about a charioteer (US poet maybe?)that includes the unclued words.
For 25 ac again there are only two words that fit with my letters, but it hasn't led to a lightbulb moment.
Most frustrating.