I have to admit that we always called the Mercury engine “a 7.7” simply because they were around 7.7 litres in volume. I was just a habit that drivers and fitters couldn’t seem to get out of! And the AV series was, indeed the engine that went in to the “Light” vehicles produced by Guy Motors. Not to be confused with the engine commonly referred to as a “240” which was fitted to 40-ish of Guy’s later offerings!!!
Couldn’t resist, Dennis!