Hi Noddy,
I don't think the early vehicles have SNs stamped on chassis. One of the first things I look at is the goal post/rear frame to see if it has a notch out of it in the top centre which indicates it's an early vehicle. There is always a chance this has been replaced but the probability of this is low. The said vehicle is lacking early goal post notch and has many other later model features such as dash, steering wheel etc.
I highly recommend a copy of this for anyone embarking on an early classic journey!
Original Range Rover
Cheers, Peter