Thanks guys, I needed some outside voices to clarify.

I love the Miyata 710, and would prefer one size down. That's why it's hard to let go of it. The Trek is great, for someone else. I'll pry my hands away from the Miyata and make room the "right" Miyata. One in a 57cm.

The Miyata 610 fits, and I'll build it, ride it, and see. It's hard to imagine a better touring bike than my Cannondale ST600. Plenty rigid and brazes galore.

I just have too many bikes. They're so cheap and finding good ones is such a treasure hunt, and I like fixing them up, sourcing parts, the whole process.
When I sold the Miyata 310, the guy said he needed a knockabout city bike, which will be served well by the 310, but it was in such NICE condition.

I guess selling will give me more room and finances to keep the treasure hunt going.
Maybe I'll find an '86 710 (with Chromo forks and triangle) in that 57cm size.

Thanks guys!

...how much would it anger the gods to use the Trek fork for a project, the Shimano 600 friction for another frame and sell off the main frame. I'd have no problem doing this if the bike were trashed, but it's perfectly serviceable to someone.