Camera with long film gate for conversion

[panF]

I'm planning to build a panoramic camera by extending the film gate of a suitable camera. Can somebody recommend any camera with a long film gate which can be chopped off to expose a longer sized negative ?

Here's the pic. of such an example but I can't remember which camera it was. Seems to have quite some space to grind. Are rangefinders easier than SLRs to modify? FED/Zorkis have that extra space but do you have any other recommendations?

Thanks