Jake,
I concur with Doug. Granted, the 6400 I have is 7 years older than your truck, but it's still got 4 corner drums and I didn't have to install a proportioning valve of any kind. We wound up taking the power brake system off an 81 1-ton Chevy Suburban and fabricating a bracket for it to mount it under the cab and we just plumbed new lines and ran them. It was nice because the truck originally had a hydrovac and the M/C was a power unit, so it still stops extremely well. It was definitely worth the minor hassle. -Jake Schaeffer
