Re: HSS to SSS conversion
I did this exact conversion ... I bought a (new) Hiway One Strat with a bridge humbucker because the price was right, although I have no use for a Strat with a humbucker. I purchased a brand new Hwy 1 S/S/S pickguard and bridge single-coil pickup from The Stratosphere, transplanted all the electronics and two single-coil pickups from the original 'guard to the new one, installed and connected the new bridge single-coil, dropped it into the guitar and that was it, job done.
If you can solder, it's a simple excercise, you won't have any difficulties.