bigger rear disc in rear than front a problem I assume?

It'll help to know what size tires you're running on the rear compared to the front. Pro-street Mickey-T steamrollers on the rear will be less likely to skid than pizzacutter polyesters on all 4 corners.
Agree. I had tiny stock Girling dics on the front, and JFZ's on the rear, and it stopped great..... cause I had tiny front tires and 14x32 slicks in the rear. (Without a proportioning valve, just a line lock).