Recently, I found an archived post about adjusting the original heater control valve. Figured I'd try it, and it worked like a charm. To add to Dave's original directions, as forwarded by Lucid, the Torx screw head is on the rear end of the valve. Turning it clockwise cooled the outcoming air right on down.

This was most satisfying, and easy to do once the valve was free of its mounting. I'd recommend the effort to anyone that's being roasted, as I was, with the older-style valve refusing to admit anything but hot air.

Speaking of hot air, that's about all...but my thanks to both Dave and Lucid for their excellent assistance,

Brendan.