Well, after a lot of looking, I ended up getting a '99 Chevy Astro, with their 4.3L "Vortec" V6. It's only RWD - I didn't want the extra mechanical complexity of the AWD version.
It's pretty nice for a small van. Less than 42K miles, and it's the LS version, with most the bells and whistles. It's obviously not as nice a ride as the Mark VIII or T-Bird, but better than your average van.
So far I've recorded a solid 21 mpg highway, but I'm sure my daily driving will be less. One thing - the steering on these vans has virtually no feedback at all - it's way too light for my preferences. It tracks and drives perfectly straight, but the slightest nudge on the steering wheel gives no resistance, so it's a little too easy to turn when you're not paying attention. Ford/Lincoln definitely got it right with the steering feel in their T-Birds/Mark VIII's.
It also has those rear "dutch doors", where the top half opens up and the bottom has two half-doors that swing out. I'd rather have just regular swing-out doors, but it is what it is. I also need to look into replacing the struts that hold the top half up - it doesn't stay all the way up right now. And while the factory stereo/CD works fine, the speakers leave a lot to be desired. 'Going to see about better speakers and a sub to fix that.
Anyway, here's a pic, (and I'm definitely still keeping my T-Bird!):