Re the paint job, that isn't the carbon you can see under the paint, it's more paint meant to look like carbon. The original Cadex frames were made from roving and unidirectional tape, they have no weave.
This frame weighs 1.660 grams
An 80mm fork will probably screw up the geometry; slow steering,
I think 63mm is the max you'd want to put in there.
As far as the discbrake adapter; ofcourse you can put one on, but
you'd better search for a post '97 Giant MCM with discbrake mounts