Quad exhaust= no spare tire and major sheetmetal work to undercarriage.
But then, you know that!
I would put a front lip spoiler from an aftermarket company (lots of choices) and m-technic rear w/ driver side m5 exhaust... And call it a day.
Just my $.02
'99 BMW 540i6 (black on black)
'99 Lexus Rx300