UCI prohibits 650c fronts. All of the races you would compete in (unless you're seeding for national team or international competitions) are governed by USAC, not UCI. All national team qualifying and international qualifying races, must meet UCI requirements and as of Jan 1st, all NRC races have to meet UCI too.

I doubt any of the above conditions apply to you. You'll probably be okay for an open training, but I would ask before showing up to a race with one.