Hopefully not too much of a digression, but here's a photo of another iteration of the Teikoku Dempa/Clarion intercom/interphone box.
This is an original period photo from a small hand-made booklet of data and advice put together by Nissan's Works competitions department at Oppama, and sent to the de-facto competitions department here in the UK in May 1974 (by then based at Nissan UK's Worthing HQ) with the intention of informing the UK competitions staff about details of the new P710 'Violet' Works rally cars which were - at that point - being shipped to them.
The intercom/interphone unit is very similar to the one seen on '7924', which was built in mid 1972. It has the same volume control (interestingly, for a 'new' and supposedly unused car, the control knob appears to be missing as it is on '7924', which makes me wonder if they were prone to falling off, or just not fitted...?) and it also has the external 'floating' jack boxes, but with some extra belt-and-braces suspension for them.
So, an indication that the Works team carried on with the same basic design well into 1974. I guess that Teikoku Dempa must have made a fair few of them?