Pfarber,
Thanks for taking time to reply to my too-long rant. Master cylinders for similar Chevrolet trucks seem similarly hard to find. A problem with mixing and matching is that the dual master cylinder also controls the clutch, so bore and stroke on the clutch side need to be matched to the slave cylinder to provide appropriate travel distance. Strangely, the hydrovac unit for my truck is easier to find than the elusive master cylinder. I am familiar with the GMC 6066 Forum where I have learned much to help with my 1964 GMC pickup. It looks like I will be going to the local Napa dealer and hope for the best.
JRMunn
