bobspets, you are correct that your headshell is not original for the PS-X7.
The original headshell for the PS-X7 was the Sony sony SH-145. In black, to make it go with the black carbon fiber arm.
The PS-X6 had the silver version. See the pictures of Balifly and Blue Shadow above.
See these TheVintageknob pages:
http://www.thevintageknob.org/sony-PS-X6.html
http://www.thevintageknob.org/sony-PS-X7.html
You also see this headshell type in the catalogs from 1978 for the PS-X4 / X6 / X7 heasdhells:
http://wegavision.pytalhost.com/Sony/1978/sony78-34.jpg
http://wegavision.pytalhost.com/Sony/1978/sony78-19.jpg
http://wegavision.pytalhost.com/Sony/1978/sony78-16.jpg
Your headshell is the Sony SH-135.
It can be found on some entry level models like:
The cheaper PS-2350 from 1975/76:
http://wegavision.pytalhost.com/Sony/1975/sony26.jpg
The cheaper PS-T1 and PS-T30 from 1978/79:
http://wegavision.pytalhost.com/Sony/1978-1/Sony7879_14.jpg
http://wegavision.pytalhost.com/Sony/1978-1/Sony7879_15.jpg
This headshell is very simple and light, but I think it is just a piece of bended sheetmetal and so it might probably not be the best in resonance supression. Just like about any SME headshell it will fit your arm without problems, as long as the combination of headshell weight + cartridge weight is within the range of the counter weight, i.e. as long as you can adjust the position of the weight so that the whole recommended stylus force range is covered, you will be fine.
The more expensive models like the PS-6750 and the PS-X models did get fancier headshells like the SH-145, SH-150, SH-160, SH-165 and the SH-156. Often there was a combination of a very light metal (like magnesium) shaped for maximum rigidity to suppress resonances, plus added convenience like a overhang scale topped off with flashy looks.
