I personally don't think a centerline smoothie looks much like a steelie with a center cap. I've seen people add center caps to the smoothie but that's a fairly involved mod for many to tackle and still doesn't look like a stock steelie.
6" steelies aren't that expensive but are getting there....most went to scrap a long time ago...but have you looked for 7 or 8"? They sell for good money for a 15" steel wheel.... now picture a 20x8 and 20x10 steelie....deep dish in the back...nice lip in the front. That'd be sweet