Does anyone know or care to speculate if the "stow-able or folding" rear rudder pedals from an L19 would fit on the right side in a 170B

I would speculate not at all.
The L-19 shares some parts with a 170 but is still a very different beast.
You'd have more luck looking at a set from a 140 or a 180.

Ok, do they fold I'm only familiar with the L19 ones

No, they will not fit without major alterations/modifications. They are extremely different from each other in form and function.