I checked out Kim's excellent J8 document here:
http://www.pentax-manuals.com/repairs/j8service.pdf
I have a black version of the leftmost one, no tab and whole body rotates during focus. focus markings are engraved.
Mine front focuses at 1m, but I can correct for it by focusing properly, then either backing up an inch, or if already backed up, just by focusing a few degrees on the close side.
I tried to take mine apart, but with hand pressure, it is too tight, not sure if the previous owner glued it down, but I would need Channel locks and a rag I think to open this up.
If I did open it up, and put another shim in there (which I don't have) I'm wondering what would happen at 2.8, 4, and 5.6.
If the shift is like the Zeiss 50/1.5, which optimized for 2.8, front focuses 6 inches at 1.5 and min. distance, then I'm possibly already optimized for 2.8.
If I shimmed it, what would happen to infinity, which currently seems on?
I'll have some M8 pics of the cat the next time I pull the card out.