Power Steering Problem

I installed a March Serpentine kit on my 1962 Impala. The Impala came wtih factory power steering. I think back in the day it was called power assist.
I rebuilt the power assist because it leaked. The unit was adjusted according to the rebuild instructions, so the cylinder didn't go in or out when the car was running. When I attached the cylinder, and started the car, everything was good until i turned the steering wheel. It spun the wheel back and forth until I shut off the ignition. The March System came with a GM Type 2 powersteering pump. Is this pump making too much pressure for the power assist unit? Any help is appreciated.
 
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