The OE tensioner bolt is literally bent at the halfway mark, even when I casually tighten it, because it was fighting the belt's tension. That was dumb of me, but then again, the bolt was already somewhat on its way out.
The 99343-11570 V-belt length is considerably shorter than the aftermarket Napa version that was on there, leaving little to no room, and it took some doing to put it back on the pulley alone.
I switched to the longer bolt you see in the picture to give me enough travel to tighten it enough. The alternator is a reman Denso, so how it fits and sits also influences the physics, which is super weird to me.
What I noticed is that the old belt was dancing quite a bit; that's how this all started in the first place, but I couldn't tighten it because the bracket had no room left (Josh can attest). With the new belt, it sits on the pulley correctly and doesn't wibble/wobble when the motor is running.
Here's the old one:
I went for a 30-minute drive around town and the back roads, revved it to 3,000 RPM, and it feels fine, runs fine (shrug), and the motor feels responsive, though again, it could be my imagination.
Interestingly enough, earlier when I was talking to Jim, I was looking at his rig's belt; that thing was sitting tight, even though he has a different alternator and his own bracket on there. The V-belt took some effort to push down with my thumb; the 90-degree twist test was snappy, which is where I am now. That's my benchmark and what I've read from the mud posts.
If any of the above sounds wrong, y'all tell me, I'm a noob.