myarmor,
Short answer: NO!
Long answer: The magazine tube is longer on the Pardner and therefore the barrel ring is farther down the barrel. The Pardner barrel ring will not even reach the magazine tube on a 870. As far as everything else goes it's almost an exact copy, almost. If you happen to see a Pardner Pump at a Gun Shop, have them place the 870 next to it and you will see right away the magazine tube is different.