Parked for a Long Time !!!

[Already Gone]

I came across a 64 Impala Wagon with 91,000 miles that is for sale. I went for 3 hour drive last Saturday to see it as the older farmer that owns it doesn't have a digital camera. He bought the car used from his local Chev dealer in 1969 or 70 and drove it till the cops told him he needed a muffler on it, so he decided to park it and as he said " I went to town and bought a new Buick". He said its been sitting for at least 20 years and it could be 25.. He just drove it in the shed ( which he needs now, thats why he is selling it) and turned off the key and walked away. Okay now for the help. He poured some gas in the carb for me and the motor fired up with no obscene noises. Its a 327 with a 4bbl and the car is completely stock. What am I facing to get this thing driveable? Will I need to remove the gas tank have it cleaned before I put gas in it and try to start the car to let it run. What about the transmission, will a service be okay on it or will I need to rebuild it. If anyone has had any experience dealing with a vehicle in this condition I'd appreciate some advice. I know this has nothing to directly do with our trucks ,but maybe someonne will be looking at atruck in this condition one day.