Good as new!
Not bad at all for a 20+ year old frame.
Have you heard of electrostatic cleaning
alloy to start with?
It is an electroplating shop process and gets rid of all impurities in the outer surface of the alloy.Looks like new.
Anodising also would preserve it to some extent, but may not preserve the brilliant sheen.
I have just been given a frame 91 GT Zakar maybe? H2A01605 inside LH rear dropout and no other id on the dropouts.
Cable abutments are sq section, but seem screwed on, not welded. Apart from that, it is as yours.
Rear brake must be the old GT Timberline Exage U style as the axis points are outside the 26" wheel circumference.IE above the rim near the GT - Z distinctive frame fork bridge plate.I was not sure about this, but I picked up some green anodised frame GT Zaskar pics from the net that shewed the old Deore canti brakes. I thought it may have the early ' cantilever like an 85 chromed Mongoose ATB has.
Can you tell what year it is by the frame number above?
Here is the green frame from the net and some comparo of later brake setups.