Yes, that does rather look like a connection for a slide mount radio and a quick google for the CRX74 has some images with "slide out chassis" marked on the surround to radio. Unfortunately I've not been able to find any further details of the Clarion slide mount for you. *Edit* Is there an appropriate connection diagram on the
https://www.tehnomagazin.com/Auto-radio-car-connector/CLARION-Car-Radio-Wiring-Connector.htm webpage labelled as CLARION CRH71 PE-9411A? *End edit*
Back in the late '80s I fitted two different Blaupunkt slide mounts. If I remember correctly for one of them you removed the existing connector block from the radio and fitted a special slide mount one that mated with the fixed chassis. The other added extra length to the radio body with the adaptor so you could just remove the adaptor to get to the original connections.