741 or 741B: What's the difference?

[jkjoller]

Can someone please tell me the difference between a 741 and 741B?

Also, do you date your bike off the frame number or engine number (they don't match). This would be for a 741.

Thanks.

[c.o.]

I've always been under the impression that the "B" stood for battery.

The engine and frame numbers would have originally matched.