I'm actually bringing a 1965 T-bird back to life as we speak. The 390 is good engine, but thirsty. Even if it sat for 30 years, if it has good compression, it will run smooth all day long. You'll want to check if the heads have been rebuilt at some point with valve seats for unleaded gas.
Keep in mind that the T-bird is a cruiser. They arent hot-rods. They were built to roll in style. Low and long. They also were pretty much the top of the line Ford in America, so they came with a ton of comfort options.
Plenty of places are making the hard to find parts.
Thunderbird Headquarters Ford Thunderbird Parts
Bird Nest 1958-66 Ford Thunderbird Parts