Don't know if this is usefull, but a gentleman by the name of Charles Semmer has a book out on Remington Double Shotguns.
His address is: Charles Semmer, 7885 Cyd Drive, Denver CO, 80221.
Phone listed is 303 429 6947.
This info came from an ad in "Double Gun Journal"
The book isn't cheap at $60 and I do not know if it has diagrams. But Mr Semmer seems to be the authority on Remington doubles so he might be able to provide leads or info.
I am no longer a member of this forum. Bye!