I don't recall ever seeing a motorcycle head with twin plugs from the pre war era...I'm not even sure the benefits of such an arrangement were realised at that time...Post war Harley Davidson sidevalves had twin plug heads fitted on occassion and a photo of one of those heads looks like a single!..
Even without twin plugs moving the (single) spark plug position is considered beneficial....Ian

email (option): ian@wright52.plus.com

Here's one with a twin plug head (and nitrous oxide injection!)....Unfortunately it's not an original head or a pre 45 picture but it is a pre 45 bike!....Ian

email (option): ian@wright52.plus.com