Surely for 70's punk it should be whatever bass you either find in a skip or steal from a crusty in a squat. If the tone isn't quite right, hit a few people in the face with it, the blood and skin should condition the strings.
To be honest, I don't think they actually went for a specific tone back then. They just used whatever gear they could steal or borrow, put on a long strap and hit it hard with a pick and generally abused it.