I think you purchased this off the local forums. I posted over there, I'm pretty sure it's not a miyata. The serial number seems like it's in line with Centurion's serial numbers:

http://www.bikeforums.net/showthread...=1#post2208689

Based on that, I was thinking it was an 86 Centurion (or another brand that was manufactured by Centurion).

Edit: Just saw the above post, looks like Lotus could be a match too since they used that serial number scheme for a year or two: http://vintagelotusbicycles.com/serial_number_chart.php

The lack of mid-fork lowrider bosses rules out a lot of mid-80s touring models that had three bottle cage mounts. I wonder if the fork was a replacement? Curious that it only has one set of rack/fender mounts at the rear dropouts too.

Whatever it is, it looks like a pretty nice frame. I'll be interested to see what everybody else has to say.