I'm seeing IN6309
Printable View
It'll be easier to start with what engines your family may have owned in the past and look for a visual ID. That pattern number(?) probably doesn't cross reference to anything. If part cross-reference books using dimensions were published there as in N.A. those might help, but then how badly do you really want to know?
Bring in a metal detectorist to go over the property and you might find something much more interesting. ;)
IN could mean it's an intake rocker. - Bob