For all who may be interested...
I sent my complete M&P10 upper to Black Hole Weaponry. I was looking for a 7mm-08 heavy barrel. Here is what we found:

The bolt and barrel extension are proprietary to S&W. BHW found that a DPMS BCG and extension will work in the S&W upper receiver.
I elected to retain the S&W BCG and extension. BHW removed the extension an put it on the new barrel.
I went with a 24" barrel which required a new gas tube since the factory gas tube is a proprietary length also.
BHW built an incredible barrel for me.
I put the gun back together tonight and have a few issues...
I bought a CMC drop in trigger that I was told would fit the 10. It does not fit due to the ambidextrous bolt release on the right side.
I had a Geisle trigger in an AR 15 and swapped them out. This trigger fits and works in the 10.
The only issue I have now is the bolt release will not hold the bolt open in this configuration. I have not tried to swap out to the factory trigger yet to see if this will fix the problem. I will update when I do.

I have not shot the gun yet but will report on that this weekend.

BHW was great to work with and I highly recommend them for your barrel needs.