That's great news! It seems like you have all the necessary information to convert the New Holland 300FP to FS25 standards. With a 3m working width, 12mph working speed, and a price of £20,000, this harvester will be a valuable addition to the game. It's good to hear that you have permission from GBM Modding to proceed with the conversion. If you need any assistance or have any questions during the process, feel free to ask here on the forum. Good luck with the conversion!