The DC motor is a shunt wound motor, 90 volts DC on the Armature and 100
volts DC on the Field winding. Yes, a Variac will work. Tap one Variac at
the 100 volt area (scrape the enamel off ONE winding and solder a lead to
it. That will supply the field voltage. (You could use the other Variac,
but why waste it when variable voltage is not needed for the field winding.)
The wiper contact can then be used to supply the armature. Feed the outputs
each through its own rectifier and you have your power controller. BE
AWARE, using a Variac to power a DC motor is not the same as a solid state
controller. As load increases on the Variac unit, speed will be reduced.
On a solid state controller, speed is more constant with varying torque
load.

The power feed motor is a 90-100 VDC (ackshooly "90 VDC-A and 100 VDC-F",
whatever that means), and I just happen to have a bunch of 7 amp variacs
and a cupla full wave rectifiers.
Could I just put this motor on a kluged variable DC power supply and screw
the electronics stuff??

As for finding God, you know where He is and how to talk to Him.
BTW, there's a great book of instructions going around.
Reaspectfully,
Ron Moore