What is "full ovate"? As in oval in cross section?
I was wondering if the grip on the Martini might be pretty tall since the lever seems to dive downwards very fast and the strong hand has to be set back a ways to be behind the "tang" sight. But a Model 12 Martini is pretty small so the scale is undoubtedly sufficiently small.
My old Martini .22 (Model 1215?) had a rear tang sight as factory made. I believe the sight was a "Model 8", but memory is not infallable of course, especially mine. Not sure why you didn't simply go that route, however.