How to Search a Paper by Citation
The following worked for me:


Google "Gen. Rel. Grav." to discover that it abbreviates journal "
General Relativity and Gravitation" 
Google the journal's title to discover http://link.springer.com/journal/volumesAndIssues/10714 
Look for issue 8 in 1977, don't find anything, assume 8 is a mistake (it later turned out to be the volume, which is redundant, because everything published in 1977 belongs to volume 8)
Look for page 497 in 1977, find the result (http://link.springer.com/article/10.1007/BF00762634), namely, 



  Reza Mansouri &amp; Roman U. Sexl (1997) A test theory of special relativity: I. Simultaneity and clock synchronization, General Relativity and Gravitation, Volume 8, Issue 7, pp 497–513.


In essence, I recognized that Gen. Rel. Grav. was most likely the journal's name. (The other possibility was Sexl. Gen. Rel. Grav., but it seemed less likely, because S.U. Sexl. seemed likely to be the second author's name followed by a period.) Once I had found the journal, the year was most useful to me. I then guessed that 8 was the issue. This didn't turn up anything. (Later I discovered that 8 is the volumne.) Next, I guessed that 497 was a page reference, which guided be towards Issue 7. From their, I searched for (what I presumed was the first author's name) Mansouri, which gave me my result.