Valid questions MikeMelb!
The pictures below will answer most of your questions. I am not sure when the Rostyles were fitted, but they were on the car and I simply left them there although there's a set of period-correct NOS hubcaps in the boot. So, Rover already had what we now know to be the series 2 or 3500S Automatic dashboard ready in 1965 for possible introduction the 2000S. I do not know why they didn't put this into production earlier, but on all the photos I have it's fitted (I cannot share most of them due to BMIHT copyright). Anyhow, the dashboard and the centre switch panel were ready by then. It's a bit different, in the sense that the ignition barrel is in the centre switch panel and not next to it or a later variant with the column lock.
As for James' book. The first version of the advertisement text was mistaken. This car originally had a Buick engine, with Rover ancillaries (carburettors, distributor, alternator etc.) and was later swapped for the current engine. The Buick engine survived, and was picked up by Richard Fishwick who put it into the car grey car wearing the Talago badges and numberplate.