Permanent magnet motors are DC motors. They are more expensive than AC motors. Since it is an OEM motor you may have to buy from the OEM, but not in every case.
I ran a motor shop for several years and we alway's had some success crossing OEM to standard motors. Take a look at the name plate. Look at the frame size. If, for example it reads 0000012356C it is 56C frame. Now if it reads 56CZ that means it has a shaft modification. Once you are familiar with the standard frame sizes and suffixes, you will get the idea. Any numbers or letters before a standard frame number mean nothing (It's to throw you off). Any numbers or letters after the standard frame size are important.
Get a motor catalog and you will find the frame sizes, with all the dimensions. Believe it or not, in many cases there is no modification except for the nameplate. If you can use a micrometer, you can tell within minutes if you have a standard or special motor.
Kjay, gave some very good information in the aspects of controlling motor speeds. Personnaly I prefer AC over DC as they can produce full torque at zero speed. Better than DC.
Check
www.baldor.com They have some online manuals for the motors and the drives. Have fun.
