[villagetinker]

Go to the Sumter county zoning office (Pinellas Plaza). If the neighbor did the arc review and there was a permit needed, they will have the info foer you to review, this is public info. If no permit required, you can go to ARC (LSL), and aski, if you have the address you can go online and review the ARC approved forms.
I believe that you can also get the neighbors plot plan (Sumter county office), which will have the setbacks shown on them.

And finial if you cannot or do or want to do any of the above, call ARC and they will investigate. Calls are anonymous as I recall.
Hope this helps.
NOTE: in some cases these setbacks are site specific, so be careful with info stating that setbacks are xx feet statements.