What you have should be a 1987 Rocky Mountain Matrix (yes, Matrix was the model name). Shimano New 105 was introduced in 1987 and was the first 105 group with SIS. That was also the year that Trek slapped an trademark infringement lawsuit on Columbus for using the Matrix name, which Trek was already using on their rims. Consequently, Matrix was renamed Cromor for the 1988 model year.

The 1987 literature lists the Matrix as being as being an imported model "built with European craftsmanship". I guess they could have changed sources after the catalogue was issued but specifying Gardin labelled forks and stem seems like a pretty bold move. The catalogue specs mention a white fork versus chrome and Cinelli bars and stem.. It sounds like this one had a major front end alteration. Often, this is the result of a crash, so I'd carefully examine the area behind the head lugs for sign of damage. Spec seat post was an SR Laprade, while a Cambino Rino sounds like it came from a older Gardin donor bicycle, along with the front end.