Thanks, sunray.
Yes, I had only 3 blank cells when I removed the last two letters of the tune. If, however, you interpret the preamble slightly differently, you get a variation...
Instead of being two letters, the last word could indicate that the unclued theme-words themselves are to go.
The preamble information, especially the parts about 'in full' and obeying both sets of instructions, is rather garbled for me! All told, it wasn't a very satisfying puzzle.