Now as for an ID on this Bianchi..........
People who willynilly go oround painting bikes should be shot!! Looking through the '85 to '87 catalogs isee no mention of Infinity tubing (until '88/89 Bianchi seldom mentions a tubing type just wether it is DB Chromoly or Columbus). I can tell from any of the pics if the tubing sticker it Infinity or not.
The only thing I can almost say for sure it it is an '87 or older. '87 was the last year for the Bianchi to be stamped in the stay caps but it is always possible that older frames or caps were used.
Now here is where things really go bad. The Premios in '86/87 appear to have nutted brakes although this could have been changed after the catalogs were printed. So it is possible it is a different higher model but which one?
I am kind of leaning towards an '87 Premio based on the DiaCompe 500 brakes w/ Aero levers and the shimano DT shifters.
Whatever it is it is sure to be a great riding bike. I like my '87 Sport SX as much as my '00 Mega Pro XL Ti.