Skullmonkeys Hints for PlayStation
1. The first 1970 is on one of the Monkey Shrine levels it is easy to get as it is in the middle of the level floating.
2. I think the second 1970 is in the second Hard Boiler level. To get it, go backwards in the level and climb up the flame-shooter.
3. The third 1970 is one on of the Monk Rushmore levels. As for the second 1970 go back in one of the levels.