Your amp looks exactly like the one in the main pic on the WEM site -
http://www.vintagehofner.co.uk/brita...stminster.html it has the same bare patch on the corner and the dinks in the speaker grill match up.
Can't find a schematic but yours looks to be the same as this one -
http://wem-owners.com/combos/westmin...tminster-1968/ which gives the date as 1959, so it's a very early one.
The schematic in post #15 looks to be about the nearest you'll find for the OP stage. I'd guess the EF86's are a mic preamp section. does it have a tremelo?
Andy.