A...there is no such thing as a 6 cylinder mustang before 94 and after ?86?...B...IT depends on what suspension stuff your talking about, CC plates, sway bars, A-arms, strut tower braces, and sub frames yes, springs and struts will fit but may not ride well...C...For suspension go and get a GT front and rear sway bar at the junk yard and some energy suspension endlinks/bushings...For HP there is not a whole lot to do to an N/A...exhaust, intake, porting....but you will spend a lot of money to still have a slow car. Save for a turbo engine, and don't turbo an N/A it will blow...
-TG
PS-try doing some searches because all of these things have been discussed before and you can learn a lot of info....