can't help you with the nitrous part. If you want one with mass air and forged pistons that would be '89-'92. Speed density was from '86 to '88 (california got mass air in '88, though) and in '93 the HO was switched to hypereutectic pistons. also i believe the '86 had single to dual outlet exhaust, unique small port heads, pistons without valve reliefs, smaller injectors and throttle body, and 200 horsepower (25 less than '87). good luck on your purchase.
------------------
'84 Mustang 5.0 LX
My car
[This message has been edited by 84stangLX (edited 06-21-2001).]