Any old encoder or how to make an inexpensive servo motor

Will any encoder work for creating a servo motor from a PMDC motor?

or

Will the encoder on this gear motor
(http://www.surpluscenter.com/item.asp?
UID=2003120116311635&catname=&qty=1&item=5-1440) work with the motor
suggested by Mariss Freimanis (http://www.surpluscenter.com/item.asp?
UID=2003070308293941&item=10-1931&catname=electric)?

p.s. How do you calculate the oz/in for just the motor from the
following?

SPECIFICATIONS
• RPM primary 25
secondary 4.5
• Voltage 12 DC
• Amps 130 mA no load
• Torque primary 33 in. lbs.
secondary 125 in. lbs.
• Ratio 620:1
• Rotation reversible
• Duty continuous