Thanks, jordan, for your kind offer at 85. PDM this morning! Theproblem wasn’t the ageism I ascribed to Sabre, but paranoia, and entirely my own. A very good puzzle.
OMG I believe I have finally resolved this extraordinary lunacy. I would not have had a cat in hell's chance without the cryptic hint from jeg. Thank you. How anybody soved it without that help is quite beyond me. I still cant quite believe the denouement even though the substitutions work including one letter which produces two different outcomes. Do you think it might have been fairer to have given us a pointer to the source. Hats off to Sabre for the bewilderment he inspired
Candledave, I appreciate the preamble and the clues are all hints is there something to be gained by reading them slowly, except an acknowledgement of my own lack of perspicacity?