I put the ER catted DP on my 340 xdrive, and didn't use any spacers. I was able to re-use the gasket and both clamps.
I wouldn't bother getting a new midpipe clamp. That's a pretty wide and robust unit.
But as others said, get the expander. I bought a cheapo unit from Amazon to help spread the pipe. I also found that once the DP was loose from the turbo, twisting it back and forth did help spread that mid-pipe opening.
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