Raymarine X-5 auto pilot
I recently fitted the X-5 to my 336 and it was fairly straightforward although the first course computer died after a couple of days (replaced without question by Raymarine, great service).
I don't know if the 306 has a round binnacle or the large box type like my 336. The box means buying and using the fitting "kit" which consists of a surface mounting post and a stainless steel ring and grommet which you don't need with a round binnacle.
The course computer and fluxgate compass are pretty much plug and play
My one is wired to a Garmin chartplotter by NMEA 0183 but I guess it will be easier to connect it to the raymarine system (seatalk) which you have.
The X-5 works well after a bit of fiddling about during calibration although I tend only to use it when motoring.
