Reference material:

The Model 1895CB octagon forend can be used on the models 1894CB/336CB but the 1894CB/336CB forend cannot be used on an 1895CB. The difference is the 1895CB forend has a routed out area to allow for the 45-70 magazine which has a bulge at the receiver end so the receiver will accept the longer 45-70 cartridge.

The 1894CB/336CB octagon forends do not have this cutout.

Hope this helps.