I can now confirm that the Sunday xi's total of 436-0 v London Maccabi Vale on 20 August was indeed a Club Record total. .
The previous best which stood for just the 95 years is actually not far behind, being 425-6 v Amehurst in Cricket Week on 8 August 1928. In those days the side batting second continued to bat once the first innings score had been surpassed (presumably to use the time till the bar was allowed to open - much stricter licensing rules than today), but this was probably taking things a little far !
Out of interest readers might like to know that the Club Record lowest score ever is held by the 1st xi - all out for SEVEN v Highgate on Saturday 23 September 1944.