Depends on what "accurate" means. A Mustang Dyno will simulate actual weight of the car plus its aero/wind resistance which is more accurate if your car is actually going down the track or road, while a dyno jet doesnt do that.
I had my 03 GT 5sp dynoed on a mustang dyno. I am completly stock and made 212.9HP and 258.1TQ. So you should probably make more than 230. Good luck. Let us know about the numbers.