It looks like you are using one of the real old style calipers and the newer style in your dual setup. I am glad it is working out for you since this is exactly what I was going to attempt. The newer MATCO single calipers work fine up to the 26" AkBushWheel Airstreak tires but when I installed the 29" Bushwheels my braking mirrors what you were experiencing.
Since the plane originally had those old style (silver-gray) round type, I was going to sell them and buy another set of the new style. Now that I read that you are getting great braking with one of each I will keep them and just get another backing plate! AWESOME!! You just saved me many hundred dollars.
Thanks for the pics ChuckG, I also decided to install the double puck from Matco on my 8" douglas wheels.
Indeed I found this thread so helpful I wanted to share some more pictures and the problems I found while installing it so it helps anyone who decides to go this way... specially for the non mechanical oriented people like me!
I had troubles to perfectly center the supporting pad with the axle so I made a cylinder to place it in to the right position. I would strongly recommend to make something like that so is not moving while drilling.
The mounting pad will only accept one position so the gear legs doesn't obstruct the brake pads. Make sure you drill it in the right position (yeap ... I miss that the first time, that is you can see some extra holes ).
I removed some material from the gear leg mounting pad and I was able to drill the 3 bolts it in such a way it wouldn't interfere with the movement of the brake pads.
My problem was other: even by getting the thing as centered as I could, the inner braking pads were touching the brake disc supports. I had to take some material away from both, the braking pads and the disc supports... did anyone had the same problem?
My understanding is that this aluminium supports where welded in the rim by the constructor and they were slightly too big (indeed one of them was broken).
As well, does anyone know where to get some brake discs? are these from Matco?