[quote name='Cairobill' timestamp='1412762716' post='2571673']
The Thunderbird is a great shape - what's it like to play?
[/quote]
Mine's a modern one (2004) but the ergonomics are pretty similar.
Due to the positioning of the strap button behind the neck heel (standard on new basses, common anti-dive modification on older ones), the bass tends to sit an inch or two to the left of where any other bass naturally hangs. This means you tend to play with a straighter left arm, and you should not try to play with the bass hanging too low if you want to avoid tendinitis. It's a l-o-n-g bass and with the strap offset it requires you to watch out for low hanging cymbals/keyboards/mic stands/band members! The strap button position also tends to tilt the top of the bass forwards slightly so you can't see the fretboard.
On my bass the neck is very thin - a joy to play if you like that kind of thing, although the string spacing is fairly close. A lot of people seem to have an issue with the bizarre 3-point bridge; personally I have no issues with it, but then I'm a finger player and don't need a "picking rest". The rich tone (on Gibsons) is gorgeous, although it doesn't do "squeaky clean" ime.
Having said all that, the feeling you get from standing on stage with it round your neck is like no other bass. You become taller, your stance gets a little wider, you are just goddam sexier!