In the beginning

[Jeff Taylor]

I posted this link a few days ago on another thread, it should help in identifying the build date of your D-shaped diff housings. I think some of the very early low frame Ruby type chassis still had the chassis number stamped into the rails, so may be worth checking out those that are missing the numbered alloy plates particularly any that don't have the two holes present to accept the riveted alloy plate.

http://a7ca.org/downloads/QuoteThisNumber.pdf

Is the first plate 233319 or 273319 ? - if 233319 it would be September 1935, if 273319 it would be approximately April 1937

277760 would be very late August / very early September 1937