OK, putting a limit on rotation turned out to be really simple, with a little research.

Thanks to an answer to this question posted on t.j.c, then sane rotation is only one edit away...

In the file /usr/lib/qt5/qml/Sailfish/Silica/Page.qml, edit the line change "return allowed" to read "return Orientation.Portrait | Orientation.Landscape". (Line #117 in my copy in 3.3.0.14 Rokua)