You will need to check with your state's motor registration authority as to what they will allow in the way of mods, especially as you're intending to change the engine/fuel system/exhaust etc. Some states have restrictions on capacity increases/ whether the replacement engine was one that the factory fitted to other models in the same range. You may need an engineers report and certification. Keeping it registered as it was before modification you will find is most likely illegal and could result in instant defect and removal off the road. I.E. being towed away. Don't want to put the frighteners on you, but you need to know this.