Hello Rick,
I looked through the "Handbuch des Grundbesitzes" and through the
"General-Adressbuch der Ritterguts- und Gutsbesitzer in
Norddeutschland, 3 Ostpreussen on the following website:
http://www.kpbc.ukw.edu.pl/dlibra/plain-content?id=67823. There is no
estate named Fristrow, but a lady, a widow
Fristrow, who owned an estate named Schoenau im Kreis (county)
Neidenburg. Next post station was Camerau.
I am sorry for you.
Kind regards
Ulrike Leo