The sticky if very full of a lot of conversation now and a few questions and answers. I appreciate it is hard to wade through but now most people simple post up their donor motor and ask questions there.
Look for a motor that is around about 9"-11" diameter and around about 12"-17" long.
It should have four terminals so that the field and armature terminals are separate. That allows you to change the direction it roates to suit your use.
If you can see the coils then the feild coils should have very few turns of very heavy copper conductors, almost like flat bar then wires, that will confirm it is a series motor.
The comm should have bars that are 2"-3" long with four sets of brushes. The brushes can be large single or twin brushes in each brush box.
There should be a lot of comm bars, around 40s to 60s in number.
The motor should have a male shaft at the drive end. A plain shaft with keyway is easiest to work with but you can use a splined shaft. If it is splined it is helpful to grab whatever gear or drive member that was on it.
A shaft at the comm end can be helpful for driving a tach or PS pump.
Look for the motor plate, the information will be helpful for major to tell you what the motor is like, he is a mine of information.
Go for a higher voltage, 48V to 80V is good as it will allow you to run a 72V to 144V pack, 24V to 36V is a little low but might be usable at slightly lower voltages. It will limit maximum potential speed.
The rest of the data may tell you the design speed, amps, power and insulation. H class insulation will allow the motor to run hotter before the insulation gives up.
If the motor has an internal fan then it can cool itself mostly. If not then look for holes at the ends where a blower fan can be used to force air in. A completely sealed motor may over heat as cooling could be a problem.
When looking at the forklift tend towards those that are front wheel drive. The rear drive three wheel lifts then to have a powered and steering wheel assembly and are smaller. However it may still be worth a look anyway.
The front drive ones come in three flavours.
One type has two motors, one for each wheel.
Another type has a motor built into the axle like a giant golf buggy axle, see my trike thread for the one I bought. The motor may not have a drive end (DE) cap and bearing carrier so it will need to be made from scratch so look carefully to see what it has.
Another type has a conventional looking heavy truck axle and is connected to the motor by a short prop shaft with UJs. That easiest to remove and easiest for direct drive to a rear axle.
If possible see the motor running. If not test the motor, when removed, with no more then 12V to see if it spins.
If you find one take lots of photos of the motor and post details from the motor data plate and maybe the forklift plate too if there is one and those who know more then me can offer specific advice.
Good luck on your motor hunt.