REAR Brake improvement - Stock disks

IMHO, two problems you're trying to overcome: the first is the factory plumbing of the non-adjustable brake pressure valve so the tiny rear calipers got full brake pressure, while the big fronts were restricted to a lower pressure. You did right to eliminate that useless valve and replumb the car so the fronts get full pressure & can function as they should. Stock front calipers are fine except for endurance track events.

The second problem is the small size of the rear calipers when combined with much larger tires. Depending on car weight, what calipers & pads you use in back, the way you drive and the traction your tire combination front & back give, you may be FORCED to use a pressure-balancing valve in the rear hydraulic circuit.

No one can predict this beforehand for any given car but a manual bias valve is an easy way to compensate, without buying a boxful of different rear calipers to find a pair that works for your combination. Expect brake pressures on the order of 1200 psi in front and about 1050 in back, in a max-effort stop.

FWIW on our street Pantera, I use 245-50 x 15" front tires, 295-50 x 15" rears on 8" and 10" Campys both with no fender flares, Wilwood Superlite ll front calipers and Porsche 911-S aluminum calipers in back, on Porsche vented rotors front & back the same size as stock solid rotors. My e-brake is a mechanical Wilwood. All hoses are Aeroquip dash-3 braided stainless steel. Pads are all Porterfield R4-S. I used a manual bias valve to balance the system initially but have not touched it in 20 years.

So drivers can't mess with it, the bias valve is in the front compartment next to the GM power booster (modified by Bob Byars at Precision Pro-formance in CA). The complete street car weighs 2690 lbs ready to drive and it stops in a straight line with no hands on the wheel.