If you get a plot number, I should be able to tell you the state of that particular section and maybe make a preliminary sortie as I have a number of other requests at Streatham. The cemetery should know whether there is a gravestone and may even dig out a sunken one for you, as I've noticed a number of recently-exposed ones both there and at Lambeth.
P.S. Just in case they're related, I have a photo of a headstone there for an Albert Barnett (d 26-Mar-1924), his son Albert Samuel (d 2(3?)-Apr-1924) and a Charles Albert (date obscured).