Just received my whiplash wheels today. They are brushed titanium. My bumpers are brushed nickel. I would definitely go with all brushed. You are making the right choice with Rushforth. Fit , finish and quality are the best money can buy. Also Jason is a great guy to deal with. Go a head and pull the trigger.
Just my personal taste, I lke the center and the lip to contrast. For example brushed center, polished lip or Powder coated ceneter, polished or brushed lip. If it is all polish, all brush, all powder coat, it loses it's detail. JMO.
If a car has chrome bumpers, door handles, etc, I like polished lips. if it has brushed, blacked or painted bumpers and trim like yours, I would lean towards a colored center and brushed lip. Maybe a silver center and brushed lip.
Like I said, JMO, and you know what they say about those opinion thingy's
I assume you've seen pics with 20s and 19s on a 68 before. Personally I think even 19s are a little big on the rears . Even on a 69 the 20s look too big to me brushed or polished