Another truly AWESOME accessory you've created there Dave. You really have a knack for repurposing Meccano gearing, discarded items and other materials!
Only thing I would suggest might be an adjustable clamping weight for the back edge of the saw blade that could be placed out near the tip, to give a bit more "bite" to the saw teeth, but perhaps that would be too much and cause the saw to dig in and jam the motion.
In any case, that drag saw is SUPER, no doubt about it!!!