Wondering if I'm missing something, would prefer not to cut access panels if I can avoid it.

Even with the bolt out you can not remove the motor and gearbox.

In the Lewmar installation instructions “a MIN of 10 cm free space

 between “ in the building Hanse put all the equipment on the deck and then place the deck on the hull and the motor is unfortunately just on the place of the wall, so they cut out the wall but just enough to let the deck down in place. There no space to take the motor and gearbox out 😡🤬🤬🤬. To takeout  you have to dismantle the whole winch from above!!!! To let the drive schaft come out the gearbox from above.

IMO you don’t have to do this bloody job to replace the original Simrad 20IS instruments.Simply unscrew the 4 screws take out from above unplug the Simnet cables ,put the new instruments like B&G Triton2 in.you need a adapter cable Simnet to NMEA2000

Simrad do not following the IS 20 series anymore 🤬😡😤

As Wild suggests all the instruments are fixed from the outside. Generally there is a bezel which is removed by levering around the edges with a flat screwdriver. Once the bezel is off you will see the 4 corner screws which once removed will allow the instrument to be pull outwards and the connections removed from the back. The GPS type screens often have just a small cover at each corner which can be removed to access the mounting screws.   

Thanks for your comments. I reached the same conclusion about trying to remove the electric motor drive part way through my attempt. I have Raymarine ST70 instruments, which I believe can only be removed from the backside, so it's looking like I'm a little snookered (and frustrated with Hanse).

It's looking like an access hatch cut onto headliner is my least bad option which is far from ideal. Welcome any other ideas, removing winch from topside is looking challenging, hex volts are either loctited in or siezed with age.

Should have been a 5 minute job....

The only other comment is that you need to look at the instrument fit carefully, as you will likely need to do some carving work on the mounting platform.  Even if its supposedly the same unit going into the same hole.   The screws may be in a different place or you need to make the circular cut-out the new square shape, etc. 

Take your time with this.   I spent 3 hours with a DREMEL tool and a vacuum getting a new windlass remote to fit in the old windlass remote hole.   

Sometimes its easy, sometimes its not.   :-)

Use a impact driver to loosen the hex screws holding the winch bases down.