I have a problem with the endgame too.
Everything seems to work if the coded word from UBOLT is entered in 1dn... that is, everything but 1ac!
For 1ac I'm left with TEOFF (I get a few names when I google it).
3ac is AMBLEMA - a genus of freshwater mussels (not in Chambers)
5ac is the same entry
7ac is KIBE
...not that we have to actually change the entry to 1dn in the grid - we just write the alternative underneath, and highlight its partner (and that's what I've done).
It looks like I'm ovecomplicating the endgame - the solution appears to be as I've said, but without the need to make new words running across (although they very nearly are!).