OK, I agree on the rears being possibly delayed due to the springing differences; but my understanding of those springs is to make sure the secondary piston comes back to the right spot like the primary piston. not to provide any timing.. but maybe not?? The force out of the secondary piston will build up to the same as the primary in a fraction of a second once both fill ports are closed. The secondary piston could pass the fill port a little later than the primary piston, but any transient difference in fill port timing would not seem to be of any use as the car's weight is not yet shifted. And the primary cannot build to any real pressure as long as the secondary piston is not building pressure.
So as far as any actual F/R brake bias, I am still not getting that with equal piston diameters....
BTW, FWIW I think some GM MC's in the 70's/80's had stepped bore sizes......again IIRC. It has been a long time....
