No worries with lead - it's not a component of steel.
I doubt you got 3 stainless barrels of that size, but it's possible. Do the magnet test. If a magnet is strongly attracted to the barrel, it's a plain old carbon/mild steel alloy. If there is weak or no attraction, it's possible that you have stainless on your hands.
Here's the real problem - the barrels are probably painted on the outside and coated on the inside. Heating them, especially with a flame source, will burn the paint on the outside (toxic fumes), and likely degrade the coating on the inside. If the coating on the inside makes its way into your beer, you'll have terrible off flavors and possibly some health concerns.
Sorry...I think I just took the wind out of your sails. Post some pictures and do a little research - maybe they'll be useful for something...