wouldnt mess up the hud to at least have a small circle thats a certain color depending on your hp left( red for little, orange and yellow for inbetween, and green for high hp, white for full hp.) or, even smaller option, just change the background color of your inventory to w/e your hp is(the normal color for full, and then have it go blue to purple to red)
or yet another option, split the fuel bar in half, and add an option to enable it even for playertypes that have it disabled. one half for fuel, and one half for health.