[CAD_CAM_EDM_DRO] PM DC Motors

I have acquired several PMDC motors that were take-outs from upgraded
equipment. These are 90V NEMA 56C frame and are rated at 1/2, 3/4 and 1HP.
The rear shaft has a fan and could be adapted for an encoder. Other than
high rotor inertia and a lot of bulk, is there any reason these could not be
used for servo motors?

My concern is the limit of overcurrent the motors will tolerate without
going poof or sucking the life out of the magnets. The high inertia can be
partially overcome with 1:1 drive but can a motor designed for more-or-less
continuous loads withstand the continuous load reversals of a servo system?

Doug