Good idea, the "improved" Permits were quite close to being Sturgeon class boats and were an overlooked steppingstone to that design.
As far as the 688s go, I thought about doing something similar but decided not to when I included the Flight II boats (whcih weren't out at all). What I did do though was include "Flight 0" which was the initial standard that the Los Angeles boats were completed to, no towed array (well I don't find good sources on this but, they at least didn't come with the retractable TB-16 + side blister and I have heard TB-12 mentioned ONCE, but other than that possibly BQR-15) as well as no Harpoon or Tomahawk capability.