Dear Cinnabar,
I agree independently with you for the first seven of the letters to be discarded from the down-clues, these being in 2, 3, 5, 7, 8, 9, 10 down respectively: but for the latter five, instead of your O F R O M, I've got D O R M S, finding these letters, in the clues to 20, 22, 25, 28, 29 down respectively. Perhaps worth doing a check of your list? I certainly hesitate to claim I'm right and you;re not; and as for using ten of these to replace letters in ten of the entries symmetrically placed,{u}and generating real words throughout - I'm still at sea...!
All the best
Doughnut