Sounds like a good price IF:
1. The gun is in the condition you describe.
2. It's not a salt wood gun.
3. The stock hasn't been cut. I don't think the black recoil pad is standard.

Even a better deal IF:
4. The gun has a long trigger tang to go with the round knob.
5. Barrels are 28" long.

Main thing is to check for salt wood. Guns made from 1967 to about 1973 were prone to having it. Serial numbers beginning with S7 (S8, etc.) through S73 are a clue to the date of manufacture.