Hi
From Info on Pitman 14000 series motors, the 14--3 motor 12vdc which I THINK may be the type of motor you have:-
design voltage 12Vdc
motor resistance 0.37ohm
Max. stall current 33A
no load rpm @ 12v 3500
This motor is about 2.1in diameter and about 4in long (+shaft), although there was a variant that had an encoder added to one end about an extra inch.
Without being able to check the motor these values are an educated guess. these motors were made as servo drive units, hence the encoder variant. Pitman also made variants on "standard" for some customers.
The easiest thing to check is the resistance, if its about right then the max current will be. The ESC can be decided from there. Hope this helps