I did just what you are saying. I built a bracket from 3/4" X 3/4" aluminum angle, lots of pop rivets, a couple of screws, nuts and washers and a rubber stopper.
So far the bracket works well and the antenna picks up more signals than the Concord did. However, the amplifier for the Concord antenna does nothing for you on UHF channels where most of today's stations are located and any antenna that does have an UHF amplifier will probably out perform the Concord. In fact, a few years ago the Concord people told me to just bypass the amplifier.
One thing I found out when I connected the Jack is that I had a bad cable and could not power the Jack. I removed the Concord base from the roof, pulled a bit of slack out of the existing wire, cut out the bad portion and replaced the cable ends.
The reason I have a rubber stopper in the list above is that the arms wanted to go over center when the antenna lowered and it could not over come the over center force when I tried to raise the antenna. The rubber stopper is placed on the bracket so it hits the antenna leg just before the antenna drops to an over center position and stops the downward motion. The antenna also does not rest on the roof bracket the way the Concord does.
Pete - Full Timing
2000 Country Coach Magna 40', CAT C10, #5892
2006 Jeep Liberty