Small update on the whole brake prop valve situation:
Apparently, EG6 prop valves could also work, as they don't have ABS and 262/242mm rotors in the front and rear, just like our M-chassis Civics.
So, if that's true, you could get a brand new valve for less than $200 from Japan. Part number for these bad boys is 46210-SR3-013
And you should be fine sticking with your original brake master cylinder + booster!
But if you've got 242mm discs all around instead you'd need a "1725" valve (46210-1725-XXX) off a Del Sol, not off an EE/ED/EF Civic! (Different f/r rotor sizes)