Since Dan has started down the road of trying to understand our relationship with the Kovno Rav, lets start with this biographical entry from the Eilat Gordin Levitan archive.
He had four children; Son Benjamin Rabinowitz was murdred in 1906R. Zvi Hirsh Rabinowitz died in 1909 his two other children; a son died at age 40 and a daughter Rachel who died in 1876.
Notice no mention of the Gonif, who would have died around 1855.
Here's another page from the Kerenets section of the Levitan site that has a lot of stuff on vartious Spektors who fill the gap between 1880 or so and the Holocaust:
So how and why did some Spektors become Rabinoviches and how does all lof this relate to Joseph Rabinovich deciding to pull up roots and head to America in 1874, which seems very early. But hey, he must have been the smart Rabinovich/Spektor.