You have three options that I can think of. Other than cost, one concern is the existing mounting plates. It you want to use the same bases, you will need to have a new rail fabricated.
If you want to use the old rail, you will need to have the vertical supports shortened and relocate the bases.
You could remove the old rail system completely and install low grab rails, perhaps several.
In the last two options, the old bases will have to be removed and the holes filled and gel coated. In addition, if any of the new mounts need backing plates, it may prove quite a challenge to add them in new locations.
I would probably chose to use the existing bases and have a new rail made or possibly use the old one with it being modified for new supports.
The newer model 180s have low rails and in theory you could order them and have them installed but again, the old mounts and holes would have to be addressed.