Hi cflight,the savage has a long drive axle with a pin then a long outside thread ,looking at the heng long drive sprockets ,the axle should fit ithrough the sprocket with a lock nut attached just like the wheel fitting minus the hex nut,looks like an easy fit once i have work it all out,i mite have to exstend the drive axle trying to look for the best idea and the easiest install and reverse design, sounds like you have it all covered i like the wheel stubs, if you use a box section and bend it into a U shape turn it on its side,with a small tale one side, fit the axle stubs wheel collet wheel collet fashion the spring action in the box section should act as suspension,at the rear of the box section you could cut a groove for the stub axle attach a shock and this would be your track tensioner,to mount the sprocket use round section welded to the box sectionwith ceramic bearings holding it in place,torsion bar job done. what do you think,it closely follows your idea,as a bonus if you mount an idler wheel on the front of the U-shape you have a natural ski shape which would ride your tracks up onto and over the snow or soft mud.
Rick.