No, the capstan from the current model pullers will not work with the older style motors. The way that the capstan attachs to the drive motor is different from each revision of the motor.
No, These ratings are the maximum rating for each of these respective units.
For the CP10K puller, we list the pull strength as 10,000lbs. This is the maximum force the puller can pull for a short amount of time, normally 5-7 minutes, before the unit should be shut down to let the motor cool. For continuous pulling, this unit can pull 8,000lbs at a consistant rate without overheating the motor.
For the CP800 and CP8000 series pullers, the maximum pull strength is 8,000lbs with 4,000lbs as the continuous pull for. Same thing as the CP10K. If the unit is being ran at full strength, then it should only be ran for a short time per pull and allow the motor to cool.