Would I sound thick if I said I was not familiar with Sandel???
Anyway, never heard of Sandel - but I'm guessing it's just an avionics brand name, and what you're really asking is if it's possible to fit any HSI to a PA28?
If that's the case, British Aerospace Flying Club, who hangar their aircraft in the hangar where I work, have two PA28s, both equipped with HSI and RMI.
Hope that's at least a little bit of help?
FFF
--------------