CCX is indeed Contemporary
All their numbers started as CCX3-3XXX they may have used a CCX3-2XXX for the 289? Dunno......
CCX frames were capable of conversion to alloy but lots of work and of course would not pre-date 1980.
COX = Valuable.....
Depends on the $ing as to what you should do.
If its a car that is COX and can get FIA papers it has 6 figure value.
If it is a CCX you may want someone to look at it to validate what you have.