Welcome back sir! I did a bit of searching through Stovebolt and only found a few tidbits that might be pointers toward answering your question.
This early post talks about when Chevy first introduced "hydraulic brakes". Seems 1936 Trucks could/would be a starting point to see about what was used on those trucks.
A peek through the web found a similar discussion in
another very long ago conversation on a 1934 1-1/2 Ton truck. Again, really only a pointer to when Chevy began installing hydraulic brakes.
Perhaps some of our fellow Bolters into
Early Bolts will come along and share further info or suggestions.
If it's of any help, here are links to the Chevrolet Truck data PDFs for
1934 and
1936 that may prove useful when trying to come up with a solution to your conversion. These documents contain engineering data and specifications to a certain extent that may help you out.
