Thank you LRF. I took a close look at the mount and it has two notched out grooves in the base plate indicating a slightly different slide on mount. I hesitate to change the base mounting plate as the person who installed it attached it with precision and love and the way he cut out the stock to accommodate the plate is perfect. Judging from the mounting holes in the plate the screw holes and locating pins are slightly different on the Ebay unit.I do have photos of the mounting plate but no way to post them.
Thank you again for your help. I must keep looking. Tomorrow I will call New England FA.