Topica hosts a couple of Guzzi lists-
http://lists.topica.com/lists/mgcl/
Also, the Guzzitech list mentioned earlier should be very appropriate and helpful.
First things to check: apart from std. stuff like carbs, also drop the timing chest and throw out the old timing chain tensioner. Put a new one in there as the old versions tend to lose rubber into the oil system.
Clean out the crankcase pan, clean out the wire filter and replace the oil filter (by '79, I think they had an oil filter but I'm not positive). Heck, replace all the oils. I think they were using nikosil cylinder liners by '79 also, so you should be good there. Check under the rocker covers for rust. Grease up the electrical connections....and see if it goes. How much you work on it and replace is kind of a function of how much money you want to spend and how pristine you want it to be. The T3 is a great bike- I hope you enjoy it!
J