contact apexxpress on snowest he is the MCX US distributor and he has been making a few tunnel dumps with mufflers. Have to modify the stock tunnel cooler as well though.
i eventually bought the CR dump kit, was going to fab my own up but never seemed to get around to it. Did not put a muffler on it, bit loud in the trailer and on hard pack but no issues in the snow or when its moving. I am sure you can just buy the block off plate from them. I wish I would have dumped it the day I put the turbo on!