Definitely an ST series touring bike, and looks very original. Certainly a pre-'87 based on top tube decal, likely earlier than '86 due to metal top tube guides (a good thing).
Size guess would be a 25" frame, but that's BB to top of seat tube so probably fits like a 58.
Half step plus granny gearing, 27" wheels.
__________________
Hard at work in the Secret Underground Laboratory...