Hi durban--yes the last bit is quite a head -scratcher. I will assume that you have decoded the grid correctly, and that you are left with word / 2-digit number / three words / 3-digit number / three words ?
A 38 item sequence starts with the 3-digit number mentioned above (which is in the form YZZ ), and you should find that the last number is a prime number under 20 . Then, remembering to leave the circled cells intact but erasing all the others, you should be able to fit everything in neatly.
Quite a breathtaking construction. Hope you get it...