I know, I know, if you can't say something nice don't say it at all.....
But Gumby, while your frame design is great, it has nothing whatsoever to do with the piece it surrounds, at least in keeping with period style. Sorry....
And yes, mats were invented by 1871. But the majority of framers had little if any use for them. Most pieces were presented, still, right up against the glass, and framed to the edge of the piece.
Pieces were presented with paper mats however, and it would be entirely appropriate to mat the piece with a nice "olden" colored rag mat. Maybe with straight cut edges instead of bevels.... and maybe even with a little embossed line edging surrounding the opening.
Probably not entirely period appropriate but acceptable and beautiful... the addition of a gilded edge or fillet around the opening... Or a few ink lines...
You could certainly get away with a nice fabric wrapped mat as well - linen seems like the obvious choice. Also, while perhaps not entirely period appropriate, a gilded fillet. Many many documents and works on paper are presented this way in important museums and collections.
Wrapped liners, sure they were used sometimes too. Mostly hideous velvets...But this is 2010, and the introduction of lots of wood into your frame package can create some issues with the ultimate conservation of the piece. There are ways to deal with that - but I'd use a mat......