The best guess as to Masi tubing is to look at the fork.
That will tell the tale of Reynolds or Columbus for the most part. Imperial oval, Reynolds, Continental oval, Columbus.
In the Carlsbad days, Columbus was a $25. up-charge and not advertised.
In Autumn 1976 I wanted a Columbus Masi, was advised it was not available at that time, Mario was out of the building.
Rob Roberson's build lists provide some light during "the Ranch" interval.
A few of the Columbus bikes received Columbus transfers. Not all.
Remember, Reynolds was cheaper. When demand was strong, no need to market the more expensive tubing.