So, once again, thank you to everyone who chipped in with their thoughts and confirmations. It definitely was the alternator tensioner bolt, and while it was okay, the little bolt that holds it in place (through the little block with the bolt-hole), well, it had snapped off or worked itself out. Whatever. Can't quite remember what John said it did.
Bolt gone - alternator belt loose - water pump belt loose - both worn, so this has probably been a while in the making.
Right after the bolt went POP and fell out onto the road, water temp spiked (but we pulled over right away, so no engine damage from that). After I stopped, started van up again just to see/hear what I could, belt squeal, immediately shut off engine. Underneath, difficult to see what's going on because I have the bash plate under the suspension arms (I can't look directly up into my 'belt-area'.
Where did I go, and who did the repairs? John and his crew at
E4 Auto Repairs (just outside Duncan), also known as
RaddCruisers (bought them out a couple years ago). Great bunch of guys, working on nothing but JDMs, very familiar with the Delicas. He even pointed out a couple of the things Glen and the boys at CCAutos had done when the vehicle was imported and serviced. Spot on! After the repairs, John even identified what was coming due, so I've got a list for next time I've got some spare change laying about the coffee table, begging to be poured into the van.
So, bolt replaced, belts replaced, couple of other things done that I'd asked for separately (preventative, not corrective), and I'm back on the road down to Victoria. Van's running great, water temp is now back down around one-third scale reading (I suspect that bolt was falling out for a while, what with the temp higher than usual and the belts being worn like he indicated) and it never even climbed above half while I was humping it up the Malahat. Price was good too, couldn't complain about that in the least. All-in-all, I'm happy, got my van back, found a place just a bit closer to home for those things I can't do/don't want to do myself, and now we're ready for next week's camping trip.