The fourth one down is the plug for the remote on a Revox B77. I was going to pay a fortune for one and devise my own timer record function, and then a guy on ebay in Strasbourg sold me the complete remote for a tenner more: Strange, as the UK Revox people wanted to charge me £160, if, and when they could get one ( I didn't like to mention that that's about what I paid for the B77).
Had you thought of mounting the rest of your kit on a trailer? - Could be the only way to get it all in - I'm pretty clued up on trailers these days!