Fox Collectors

I recently purchased a 1913 Fox Sterlingworth 12 ga. I removed the stock and did some cleaning without completely taking the gun apart (using the excellent instructions found on this site), however as I am attempting to re-assemble the gun I am having significant difficulty in getting the floor plate to completely seat. It remains about 1-2 mm high (equally on both sides) just beneath the sear pin no matter what I do to try and seat it. Does anyone have a suggestion for what I may be doing wrong? Thanks so much for your help

Check to be sure the sear pin lock screw is not protruding above the boss in the frame. Also that the stub beneath the safety slide is not catching the push rod in the stock. Lastly, it's a long shot but check that the sears are not re-installed upside down and crossed over from side to side.