Not really a muscle bike, sting ray, guy...but, I have read some pretty good web pages describing the difference (that I can't find now) and can try to relate what I think I remember
. Hopefully the real MB/Sting Ray guys can shred or verify the following...
The quickest way to tell visually is the joints. There should be no weld beads visible, nice smooth radius transitions everywhere. That will weed out most of the reissues. Also, the bottom bracket. These were made out of sheets of stock and pressed into shape...so, on an original there will be a seam going across the bottom of the hanger...also, the chainstay to bottom bracket transition is not smooth on the originals.
The exception being the '98/'99 reissues, which I believe have the brazed look at the junctions. I believe they also duplicate the rough transition at the chainstay. But, I believe they don't have the seam on the bottom of the bottom bracket.
...and that is what I think I remember