If your model 400 is a semi auto shotgun, with a squarish back to the receiver (something like the Browning Auto-5) these were made for Western Auto by Savage/Stevens/Springfield, and should cross reference to the Mdl 745. The e-commerce side of gunpartscorp.com has a schematic for the Savage 745/ 745C, see if that looks like yours. They DO have some parts available if needed.
Mossberg, Model 400
100-400 or so
Mossberg
Mossberg
Mossberg
Made for Western Auto by Mossberg- their model 353.
Browning never made a model 400 semi-auto shotgun.I believe that your shotgun might have been made using 1 of john brownings Patents,which would require that the patent be posted on your shotgun.
I think Savage did. sorry it was not a savage. the revelation model 110 was a marlin model 81.
It' a Savage model 94D
Revelation Model 107 was made by Mossberg (Model 640K)
Mossberg
Marlin