I've done 3 events so far. Being an HPDE kind of guy it wasn't a huge transition, but it was definitely different. I don't know what type of layout your event will have, but it's going to be hard not to fail with an open diff unless it's very low speed stuff. I'm using a welded 3.46 and it's been working very well so far.
What suspension setup are you running? Lower and stiffer is better, especially for that open diff. Since you can't power over or clutch kick it to initiate the slide, you're going to have to carry a lot of speed on entry and you'll have to flick it to get the rear end out with momentum. If you have absolutely no drift experience I'd suggest you start slow and get used to how the car feels sideways for extended periods of time.