On a 16" mid-length, will a shaved front sight base be "unexposed"  with a Larue 11.0 ?
I imagine it'll be close, barely covering it.

I found this, sorry don't know how to post a PDF. http://www.themakogroup.com/images/SpecialWeapons.pdf
At any rate, its a 16" with a 11.0 Larue and Larue gas block. With that set up the gas block fits flush underneath, but with a shaved gas block would the rail cover it ?

Can anyone recommend a 'smith for the job ?

The gas block on a midlength is 9in out (standard middy guards are 9). An 11 in rail should cover the block.