IFB for riser construction?

Could I build a riser with insulating fire brick?

I'm considering the DSR2 setup and have enough K-28 IFB to layup an octagonal riser to the upper chamber.  
For a 6 1/2" system, I calculate the inside face should be about 2 3/8 long, with 45 degree angles on each end. Outside face would be a little over 7"

Should the brick ends be clay slipped to seal, or the whole thing wrapped in Superwool and steel bands? Both?

Thanks.

Hi Randy;
IFB is top-of-the-line for risers, better but not faster than a five-minute riser!
Not having built a DSR yet I can not answer your other questions.

I will say all mortar is going to crack out in the heat of a core.

So, dry lay the bricks with steel strap wrapped around them to hold the whole thing in place?