I just measured the lower cables that I removed from my '81 R65 about 4 years ago .
One is 19.5 inches (495mm), the other is 18.5 inches (470mm) .
Up till now, I thought they were the same length !!!!!
I measured mine from the center of the swaged fitting that connects to the carb end, to the end of the smaller swaged fitting that goes into the splitter .
Just a thought, I wonder if the high or low handlebars would account for the difference in length .
Here's a little bit of information to remember, if you have a throttle cable fail, you can swap the 'choke' cables to the throttle side, and they will work to get you home .