Hotel,
My bike actually had the two adjusters you referenced above. What was missing were the two 'blocks', or end-caps that fit into the end of the swing arm. Not all XS650s had this type of design at the swing-arm end, and to be honest about it, this is the first and only one like this I've ever had. But, without these blocks, the adjuster bolts have no where to 'land' and hence nothing to push back against. So, no adjusting possible. But, I did find a set on ebay, and while I probably got gouged on them, they're now in the bike. They were actually quite easy to install. All I had to do was pull the wheel fully to the rear and back the adjuster bolts out, then these blocks just dropped in and fit into the swing-arm axle opening. Then just slid the wheel foreward, installed a new chain, and then just tightened the adjusters until proper tension on the chain was achieved. I don't know if Mike's sells these or not...... I don't recall seeing them, but I'm also not sure how hard I looked for them there. The ones I got were OE Yamaha parts, still in the plastic bags. I think I paid $12 each for them, plus shipping. But, had to have 'em!
Anyway, thanks for the above reference. Ya never know when it too will come in handy!! Tom D.