First location is the one of the book:
Reichersdorf / Niederaichbach : 48.592173352234234, 12.315283231591787 in GoogleMaps
In the text the location start:
Mosthan ("Post contracta in Mosthan") this should be on the other side of the Isar: Moosthann (today Postau) : https://de.wikipedia.org/wiki/Moosthann
Wiselsberg (the grooms fathers place "coloni in Wiselsperg") This is near Reichersdorf (south of ), todays spelling Wieselsberg 48.56545045316131, 12.372638915246625. Googlemaps
Stegbrun (the spouse fathers palce "molotoris in Stegbrun") Since the father is miller, and the contract for marriage is Moosthann it should be a location near water near Moosthann. Wikipedia for Postau includes a "Stegmühle" https://de.wikipedia.org/wiki/Postau , and Bavarikon a "Stegbrun" in Kreis Landshut. Since this is the same Kreis as Postau/Moosthan, it can be assumed, this is the place.
Hope this helps