There has been controversy about the "race only" units ever since they appeared. They claim to be "constant output", hell that's what a VR is SUPPOSED to do.
I would buy a local Standard Blue Streak and no other. NAPA and others should be able to produce a pigtail.
You can ALSO just ground either field terminal of your isolated field squareback and use the "old style" regulator. Use a Blue Streak no. VR-128 which has a different appearance than the 69/ earlier unit, but wires up the same way.
