The poster enquired re his 707 series arm, which I don't have. Mine is a G-727 Gyro Master which still has its original armlead. Female "din-type" 5-pin, metal-sheathed plug on the lead with a little locating screw on the plug. Inside the armpost are 5 "din-oriented" skinny pins.
It probably was incorrect on my part to offer this info as the 707's armlead config can of course be quite different to the G-727's