Put some electrical tape where you want it to be and drive around for a week to see if you like the way it looks. If you like it then I'd say pay someone to paint it for you and if not you're down 5 minutes of your life and a roll of tape.
For how close you could get your bumper to look like an aero I'd say work with what you got, I wouldn't be too shocked if you could put the the aero grille and fog light covers onto your car without buying a brand new bumper. Or you could go all out and get some quality honeycomb mesh and get creative.
'90 900 SPG (RIP rust)
'86 900 SPG (DD)
"A car with an image so immaculate it can hold confession and communion."