The only Lewis that I was able to locate is a George E Lewis born in 1829. He apprenticed in all branches of the Birmingham gun trade. His fame rests on his magnum "gun of the period" which was popular with generations of wildfowlers.
Values listed for guns are:
Boxlock non-ejectors $1000 to $4000
Boxlock ejectors $1500 to $5000
Sidelock nonejectors $2000 to $10,000
Sidelock ejectors $4000 to $30,000
Hammerguns $2000 to $10,000
These are the only listings that I can find. They are in the Standard Catalog Of Firearms. There is nothing in the Blue Book at all.
A 4 Bore would be considered a magnum gun. It is a huge size and I would hate to be on either side of it.
I hope this helps you,