I don't have a set, but would like to encourage you. I would just use a similar set of bars as a reference. Basically you just need to make it with a swuare tube, rather than a rectangular one. How authentic do you really need them to be if you are already improving/ altering them?
I've read you want to make the length longer to catch the spring eye. I think that is a great idea. They made them both with long tails and without. I would recommend you make the long tails. This will get you the ability to toss in a set of wheelie bars.