On my 356 I think the wiring for the radar ran between the liner and the underside of the deck. There was a junction box under some of the trim around the compression post. I think this because I remember noting that the wires didn't come up from the bilge when I disconnected them in anticipation of dropping the mast. Maybe it would be possible to snake a wire to use as a messenger in that space.
If you need help there is a guy here in G-port who does installations of electronics and other systems and has many happy customers. PM me for details.