Flamegrower said:give a bricker hammer and 4" brick chisel a try...you will be surprised how easily AND precisely it will cut those bricks......and if any of them do show, they will look more natural than a cutting tool will afford.....trust me I do a lot of natural stone masonry/veneer and with just a little practice you will be cuttin those bricks with a chisel and hammer like a pro....if you have access to some spare bricks you can practice outside on them...to get a feel for how to cut them...usually a couple of medium hits on each cut will do the trick.....keep us posted on how you make out!
thanks for this - yes many was to skin the cat here. I can actually practice on the top bricks as these will be 100% convered. It is the side bricks that might/might now be revealed. I will let everyone know how it goes (but again, Wed is the big day to see if I have the necessary clearances). I will be in mourning if I can't get the insert.

The wife is on board (after hours of me wearing her down) as long as there are minimal changes. Any work on the mantle would just cause issues.