We were working on a Norse Dark Ages game that took elements from BRP, Pendragon, GURPS/Melee and others. Like GURPS, you didn't have HP per location. There was random hit locations for armor and wounds. The base rules were pendragon, so there is no real concept of a Fumble. If I was using BRP, I'd have a fumbled CON roll mean a permanent injury (or death for head/torso wounds). Not sure if this will make a lot of sense, but here are the rules we used.
2 Right arm
3 Left arm
9 Right leg
0 Left leg
Hit points (HP) represent the state of a character’s health. When a character is injured he will take one or more points of damage and the player immediately lowers the character’s hit points by that amount. If the character takes greater than or equal to his Major Wound level in one blow, additional effects happen.
Flesh wounds are caused by attacks or other mishaps dealing damage less than the character’s MW. A character can soldier on after receiving a flesh wound and suffers no additional penalties in combat.
Damage equal to or exceeding the MW value means the character is badly injured. Minor NPCs will be out of the fight if they take a major wound. Characters who attempt to fight must make an immediate CON roll. The effects of success or failure depending upon where the blow was struck:
Head or Torso
The character is stunned and unable to perform any actions next round.
The character is stunned next round. On later rounds he may make another CON roll to become un-stunned.
The character falls unconscious, and begins bleeding out. He loses 1 HP each round unless healing is applied or he succeeds in a CON roll.
Any item carried in that hand is dropped. He may pick it up or draw a new weapon next round.
Any item carried in that hand is dropped. On later rounds he may make another CON roll to regain use of the arm.
The arm is rendered useless until the character receives healing. Any item carried in that hand is dropped.
The character falls prone. He may stand next round.
The character falls prone. He may stand next round, but MV will be at -1.
The character falls prone. He may stand with a successful DEX roll, but MV will be at -3.