1964Cuda, Thanks for the feedback. I'm unclear as to what combination valve you have there, it may be just the dual circuit distribution block with the switch in it; as was used for '67 to late '69, '70. My research tells me those do not contain a proportioning valve, and the proportioning valve was a separate piece after the distribution block before it went to the rear axle for those years (see my link in post #12 above to the Mega Parts '67-'70 proportioning valve that I have ordered). Inline tube has a video showing the changes from '62 into the '70s.