If you can spin the motor with the starter I would make sure the battery is charged good so you get the fastest cranking rpm's you can. Pull the spark plugs, remove the intake cover and spark arrestor. Crank on the motor while shooting fogging oil straight into the carbs, there should be enough turbulance to coat the crank.
Putting antifreeze in the system should be done with the motor running. If the machine is not going to freeze then skip this step. If it is going to freeze, and it was my machine, I would very gently pour the antifreeze in while cranking the motor with the spark plugs in this time so the air flow is out the exhaust instead of the plug holes. After I was done I would pull the plugs and look in the cylinders to make sure there wasn't any back flow of fluid from the exhaust.
Before you put the plugs back in give each cylinder a shot of fogging oil and a couple of revolutions to coat the walls.
Dump some fuel stabilizer in the tank and shake things around. The gas in the carbs is just going to have to go without stabilizer unless you want to drain them.
Pull the battery and give it a monthly 2 amp 12 hour charge.
This is how I would do things if it was my machine. Anybody feel free to add to it.