Here's what i did with this problem on my 52pu with drum/duum. Go ahead and use the corvette mc, position in the same place as your original under the floor. Span the gap with a bolt, washers, double bolted with a cotter key. You'll need 2-10 lb residual valves for drum/drum and the the mc will work fine if you later want to go front disks. I run from wildwood residual valves. Install the 10 lb valves as close to the mc as possible. I like the brass ones from Engineered Components, Inc Vernon Ct. call them as 860-872-7046. Ask for EC-655 3/16 brass. Verify the pn as it may have changed since 2003. I'd also get a 2 lb valve for the future front disk upgrade at the same time. Good luck.
