Is it built yet?
All you have to do is take it to a local truckstop. Most, if not all, have scales to weigh 18 wheelers for their payload.
You walk in and tell them what you would like weighed. Get two weigh slips. One with just the bike, and one with you sitting on the bike. That way, if you have a target weight in mind, you can drop some pounds to get down to race weight.