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
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.
Mossberg
Mossberg
Mossberg
Made for Western Auto by Mossberg- their model 353.
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)
I can say that the revelation model 335 was made by the firm Mossberg and Sons.You may want to contact them and see if they have the information that you seek.The Revelation name was a house brand name.
Mossberg