I don' know about the XS1-TX guards. The 74TXA, 75XSb, 76XSC Have interchangeable guards and will not fit the 77XSD and later.
The 77D, 78E, 79F, and all the Specials from 78 and later should all interchange.
You bought a guard off ebay and i assume it was sold as an XS650 guard, (Or was it sold as an XS guard that fitted the XS, 650, 750, 850, 1100), really have to do the research to find out, or ask specific questions when dealing on ebay. The sellers don't know what they are selling half the time, jumping on the XS650 wagon and hoping to make a quick buck.