Hi,

A Grebe-Eisman Synchrophase

That's a strange combo, I wonder what it looks like?

As I recall it was about 20 inches wide and about 8 deep, three tuning
dials mounted horizontally so they came through the panel, linked by a
chain drive aas I recall.

That's a Grebe Synchrophase. There was another company, Eisemann
Magneto Corp., that made some vaguely similar models, except that only
their rheostats were horizontal, not the tuning dials. Freed-Eisemann
(no relation) was also a well-known maker in the 1920s.

73, Alan