What's a gravity focus? Is it that silver/black little knob in the picture? I've got a feeling I may have a Color Pack stashed away somewhere, but I never got round to using it because it was dead on arrival from eBay. Maybe I'll dig her back out.
A gravity focus aid is a little device that uses a weighted needle and triangulation to measure the distance between the photographer and the subject. It works well in most situations. But, as it needs to 'know' two sides of a triangle to resolve the baseline (distance to subject), you need to be of average height, and standing.
Another option might be the 'face-sizer' viewfinder on some hardcases. Yours may already have a red or yellow square in the VF? The manual says fill this with a face and you are at the right distance, also marked on your focus scale on lens (if equipped that is).
As for the other auto folding Land cameras, the pick I think is the 360, but anything in this configuration will do the job! Skj.