The v-twin Blackburne was not a common engine. In Australia, manufacturers typically favoured JAP, Precision, MAG and De Luxe engines for their big twin models. The Victor Blackburne is, so far as I know, unique among Australian machines in using the Blackburne power unit. Even in the UK, the motor was not a popular choice although is was adopted by a number of the smaller manufacturers for their top-of-the-range sidecar haulers. Blackburne themselves produced a big twin machine, and this continued when they passed manufacture of complete bikes over to OEC. There are a couple of surviving OEC/Blackburne twins in the UK.
Since there's not too much material about Blackburne on the web, I thought I'd devote a little bit of space to machines that used their twin engine. The first one is from the Rex Motor Manufacturing Co., Coventry, and is probably a contemporary of the Victor Blackburne. The photo comes from an advertisement that appeared in The Motor Cycle in November 1920, and shows an "ideal sidecar touring machine" of familiar specification: big twin motor, long wheel base, and chain-cum-belt transmission (soon to be overtaken by all chain drive). Aside from the sloping frame and the Brampton Bi-flex fork, the general layout has much in common with the Victor Blackburne.
By May 1924 when the following advertisement appeared in The Motor Cycle, final drive by chain had almost completely taken over from belt for British machines. In Australia, most of the local manufacturers had stopped assembling their own machines and had gained agencies for the major British and American manufacturers who were by then dominating the market. I doubt, though, that many OEC machines made it to Australia in the mid 1920s, although a few of the later "duplex" models did. My guess is that few of the overhead valve Blackburne twins were sold anywhere, although I do recall seeing a photograph of a survivor (from one of the Scandinavian countries?) some years back.
That said, at least one overhead valve twin Blackburne did make its way to Australia: parts of an engine survive, but the make of the original machine is not known.