Proportioning valve question

jawbone said
Am I to understand correctly a smaller rear wheel cylinder will compensate as well

You can do that and through experimentation maybe come up with a combo that stops better than stock.

Or...

You can use the decades of engineering that went into the factory setup.

If you go 73 up single piston large built pattern then the 73 up master and 73 up combo valve would be the way to go

If staying sbp I would go with KH and related parts.