The 400 isn't a sidelock, but rather a sideplated boxlock--the post-Ithaca gun, that is.

Re the catalog copy posted above, the 200's were available either coin finished or blued, as were the skeet guns. Matter of fact, the only skeet guns I've ever seen (not too many, one currently at a local pawn shop but with a cracked forend) have all been the blued receiver variety. And as far as I know, all the 280's had blued receivers.