The two villages Finkenbach and Gersweiler were merged to Finkenbach und Gersweiler in 1798 by the French Administration.
Since 1818 (as result of the Congess from Vienna) the administrativ/political structure was:
Finkenbach und Gersweiler, Landkommissariat Kirchheimbolanden, Rheinkreis, Königreich Bayern, Deutscher Bund
In 1900 it was called Finkenbach-Gersweiler, Bezirksamt Rockenhausen, Königreich Bayern, Deutsches Reich
Finkenbach-Gersweiler came in 1946 to Rheinland-Pfalz, between 1816 and 1946 it was part of Bayern.
Between 1792 and 1814 it was part of the Kanton Rockenhausen, Department Donnersberg of the French Empire.
1304-1602 both villages belonged to the Freie Reichsherrschaft Hohenfels-Reipoltskirchen, Heiliges Römisches Reich. Between 1602 and 1792 the owner/ruler of the two villages changed very often.
But they were never part of Preußen, the name of the ancestry record is simply wrong, like a lot of records on ancestry and FamilySearch are incorrectly labeled.