As to the RF housing, I have no idea. I think it's all in one piece on mine, never thought of removing it. But I'm sure there are more differences between 4z5" and 5x7" than just the size.

The bellows on Technikas are very thin yet very strong. I would ask Linhof first, they are very polite people who give very precise answers.

I know that www.camerabellows.com can make Technika bellows, but that it expensive. But so is a new Linhof product...