There is nothing special about the Sotoh.
The mechanical linkage set up is conventional.
Something is broken or disconnected.
The peddle is connected to a shaft that is connected to a lever that activates the clutch.
Between, on the shaft is an adjustment to lengthen or shorten it.
The clutch spring is between the lower part of the clutch peddle shaft and a point on the floor pan.
While depressing the peddle you could feel resistance without actuating the clutch.
It might just be as simple as that shaft* (only retained by a cotter pin) has fallen out of its proper holes.
If still connected does it move the clutch lever that goes into the bell housing? if it does then there is an internal problem.
Before accepting an internal problem you should adjust the linkage length.
*Shaft is but a 1/4" rod with 90 deg bends at both ends with an adjustment device in between. Both ends simply use 2 cent cotter pins.
Good luck. (also own a Mitsu) mitsu=sotah