This is my opinion, on this matter.
My 3800 has the stock master cylinder, although rebuilt, still in use. The ol girl has had plenty of weight in her bed and stopped just fine. Brake wheel cylinders and all components have been overhauled. I never had any issues of bring her to a safe stop even during panic braking.
She has a 235cu in, power plant.
I could see upgrading if the suspension components were transplanted to a newer disc assembly.
Just my 2 cents
Jim
