my 81 G/S has always swum nicely-- the depth limit has always been the intake snorkel tubes under the tank, which is something like 2' or so vertical depth. Whenever in doubt at a big puddle, a walk-through or use of a sounding-stick has told me go/no-go.
the ign and alternator stuff does waffle a little after a deep swim, but it heats off after a minute or so. i change oils as a matter of course after such rides, and rarely have i found any water present. Cheap insurance is my take
Things that help: silicone grease packed in the spark plug connectors, and a fresh/new speedo-cable boot packed w/ same sillycone grease. That last item has kept water out of the tranny very well-- but i still change tranny and FD oils after extended swimming rides. FWIW: on an old, ratty speedo cable boot i used to get much more water in the tranny, even after a simple road ride in a downpour. A new boot pretty much eliminates that ingress
Come on in-- the water's fine
edit: per Frank's warning about the bowl vents: i have the indy floats and bowls, which don't have the bowl vent tubes. That may well make a difference in keeping the carbs water-tight as i've experienced