I just picked up a Pro Miyata (~'85?) from a forumite this summer. Set up with a Chorus triple, Cyclone derailleurs and brakes, GEL330s and Delta compatible pedals, that bike is all there. Perfect fit, handling, shifting (yes, I still do DT and with the SunTour "auto-adjust" shifters - forgot their name), it is one hell of a ride! Stiff. Plenty light though not by modern standards. All it needs is better tires. (Conti Giros on there now - they work but are just so-so. Bike is tire size limited, 24c max. Quality rubber you can run rim-saving hard is a real blessing. Very good Veloflex 23c tires are on their way. With that, bike will be a treat.
Tubing is Miyata Cr-Mo butted. That tells me nothing. It is strong. Blades and seatstays are ovalized to semi-areo and still feel rock solid for side forces.
I could argue the bike should handle bigger than 24c. Also it should have WB bosses on the ST. A head tube pump peg. But all the rest? It's all there. Ride, geometry. Those parts I just happened to have dropped right on like they were home. (I do have my seat near slammed on a SunTour 26.8 MTB post. I'll splurge and get one of those lugged steel Nittos and center those ti seat rails before I break them. But that steep seat tube isn't a Miyata mistake. I love the steep tube, short chainstay., tight rear end and it's handling, all the time and especially on hairy downhills. This bike's totally confidence inspiring anywhere.)