Im all new here and i just got hold of my third large format camera. It's a Linhof tech III (i think, since it has a rangefinder), 13x18. After messing around and googling a lot I still have a few unaswered questions, mostly about the backs and film holders. It came with two backs, one on which the focus screen swings out giving room for attaching a metall holder. The other one is a spring back that fits 4.75x6.5" (english half plate?) wooden holders.

So the questions:
1. The back that swings out has a ground glass that is very close to 13x18. The metal holders for it seems to be able to hold 2mm thick 18x13 glass plates. Some of them have aluminium plats fitted to be able to hold film flat, some dont. None of them have glass plates. 13x18 film fits ok and so does a 5x7, just slightly worse. What i wonder, what else fits in this back? Are there proper film holders for 13x18 or 5x7 that fits?

2. The spring back has a ground glass that is only one or two mm smaller than 5x7" in both directions. Im thinking there are propobly 5x7" holders that fits this back. However, i only have the wooden 4.75x6.5 and the 4x5 graflock holders to test with. Would a standard 5x7 graflock-like holder fit or does it have to be of a linhof kind?

Im very greatfull for any input!