Ok,
Firstly, I would agree, take it back to standard, did it come with 90 spec interior but 88 spec bumper / spoiler ?
Shame you cut the standard boost hoses, I have a set if you need them
Price wise, I picked up a white G reg, 50K on the clock, 1 owner from new, almost full ford service history. Full 90 spec setup. It was totally standard though, even had the original pipe on it
I picked it up for just under 3K

It is very clean, not mint, but I am a bit of a bufty and doing my underside on the car at the mo
I would say price depends on the cars history, is it fully documented ?
Also, have you had the underneath done then? Bet I can find atleast one bit of rust, surface atleast
Good luck with the sale matey.
Car looks very nice