My '65 coupe has a drain plug on the bottom of the tank on the passenger side. Yours should too. I used to work overseas and would let my 65 sit for 10 months out of the year, and got along pretty well leaving it with a full tank of gas along with "Stabil", but after a few years, the gas finally turned into varnish. Now that I'm back in the states and retired, I drive mine at least once a week, if not but a few miles and keep the tank topped off with fresh gas as often as I can think about it. So far, mine starts and runs like a scared rabbit.
Yes, blow out the lines and change the gas filter. Also make sure the fuel pump is getting sufficient gas to the carb. If not, then the pump may have gone south. Take the line off at the carburetor and have someone try to start it while you observe just how much gas is coming through the line to the carb.
Let us know how it turns out.