You'll have to fabricate some kind of mounting points. Maybe the seat bolts and something around the back seat for the shoulder straps. I bought a 5-point harness from racerwholesale.com for really cheap (3" not the narrow 2" so it's very comfortable).
The cam-lock variety is more expensive but nicer in the way to works. I just got the cheap lever locking type since I only use it once a month or so. I suppose the best you could do to match the seats is pick a color that matches or contrasts with the seat color.