The 81 is a CB650c.. The custom might be the difference. It looked like the exhaust pipe was tucked in more, the kickstand hinge was more exposed, and the kickstand didn't have the big loop on it that goes around the muffler since it looks like the kick stand doesn't tuck up behind the muffler like on my 80 CB650.. The 79 I saw looked the same as mine, but I just wanted to make sure before I bought it.
Thanks..
- Marc