The last chrome-barrel Guzzi was made in mid 1979 so anything after that will be something else. Very many of the '76 - early '79 bikes have already been converted to Gilardoni Nikasil or iron barrels. Only way to find out is test with a magnet, putting a stick magnet down the plug hole, no attraction = chrome, little bit = Nickasil, sticks hard = iron. The chrome decays with time, not mileage, so even one in the crate will start putting flakes of metal in your oil if you run it.
Other than that, they're good solid bikes and a lot of miles for the money!