Bill,
Here's a great discussion of your subject on the Chevytalk forum:
https://www.chevytalk.org/fusionbb/showtopic.php?tid/356278/Notice the give and take of information in this discussion of brake fluids. That's the hallmark of a highly effective information sharing forum.
Notice also that fluids ARE compressible despite what various "Experts" assert and despite what our high school and college physics teachers told us.
Like you I think a tandem MC is a worthwhile safety upgrade and I adapted one into my '36 Chevy PU, the first year Chevy used hydraulic brakes. There is some accumulated grime in the photo because this '36 was restored in the early 1970s and has been to a a few shows where it did fine but is mostly driven and had accumulated plenty of mileage in the last 45 years or so.
Ray W
