Ended up replacing the roll over bar for an FIA track-spec on my 310R build, so have an unused standard roll over bar for sale. Caterham link: https://caterhamparts.co.uk/road-bars/2868-roll-over-bar-de-dion-sv-sloping-metric-chassis-.html?search_query=roll+over+bar&results=513 Price: £150 or best offer. Item located in Essex. PM me for details.
I'm partway through my build, having just finished the front suspension. Having struggled with some of the inaccuracies/vagaries in the existing manual, this looks incredibly useful. There are pictures!