Rich, Are you sure it is stretch? have you laid new tracks along side the old to see if it has gained length? or possibly just wear on the drive sprocket and links?
Just curious, my Taigen Sherman lies in between your old and new pics. My PIV's look the same as Dusty's, they have just the right amount of droop over the return rollers.
On my JS2, the idler adjuster was too coarse and I had to remove a link, so I had to slot the gearbox holes to slide the gearbox just slightly forward to prevent track jamming between the sprocket and metal overhang. I've done this technique several times before when the adjustment wouldn't quite meet my wants.....
I hope Erik has addressed your needs.
Jerry Rude
Roseburg, OR