Ah! I thought it looked like a 2000TC with a V8 chin... I thought the V8 had the twin bonnet bulges, even on the Series One? Thought it wouldn't fit under the old, flatter bonnet?
You really aren't that familiar with the Rover P6 are you Richard?
All series 1 cars had the flat bonnet and alloy grille, the only panel that changed between the V8 and 4 is the front valance. All series 2 cars had the double hump bonnet and plastic grille. (And vinyl rear pillars)
The giveaway is the aluminium front lip on the bonnet that signifies V8, also the 3500 badge on the grille.
While we're at it, series 1 cars had smaller outside doorhandles (with a couple of exceptions)
All cars used the same taillights (except for pre '66 cars which didn't include the reverse light) but series 1 cars had the reflector mounted on the bootlid, on series 2 it was on the rear wing.
All series 1s had a strip speedo except for the NADA 3500S and the strip speedo continued on series 2 single carb cars, series 2 V8s and TC got the round dials.
There are lots of other minor differences but those are some key ones that I have seen you mention.