Landy hardcore

Hi. New here. I have just acquired a 1989 petrol Landrover 90 4c sw. Had a good look over. And rear cross member and front legs need replacing. Once I remove old rotten legs, and have replaced with new. What do I do about the vin number. I don't know anyone who can restamp, if allowed. Or do I leave it blank?? Also just before my purchase, the last owner converted it to a 300 tdi. But the v5 still says petrol. What do I do about this. Thanks in advance.