Yesterday I bottled my first real sour bier.  In bottling the Yard City Sour red, I chose to blend it with some Mix-a-Lot and a teensy bit o' B5.  Yard City Sour is 2.5 year old sour red produced using Wyeast Lambic Blend with a terminal gravity of 1.006.  Mix-a-lot is a hodge podge blend and feeder that did well at 1.005.  B5 is the  the club Strong Dark Belgian, that is the "Big Beautiful Belgian for the Bourbon Barrel" with a gravity of 1.013.  They were blended as follows for just under 5 gallons total:

1%   B5: for it's woody character & some tannins and the tiny bit of residual sugar.

              It's a 9% abv bier.

8-10%   Mix-a-lot: for complexity to the blend, differing sourness than YCS, & body.

The rest:  Yard City Sour, 'bout 6.7% abv

Bottled with Red Star Champagne and sucrose to about 2.7-2.8 volumes.

I used a 6 gallon carboy in blending.  (I really had to think this out!)  First added B5 and yeast and sugar to carboy.  Racked Mix-a-Lot portion onto that with CO2, and then the YCS with CO2.  Racked the mixture to the bottling bucket.  It looked like it was well mixed.  I hope the blend does well.  I'm thinking it could take several months for the different beers involved to mingle.  Plus, the tiny bit of residual sugar in B5 that will be continue to be fermented will add to it's progression in character over the years.