Day-
I would normally suggest dry ice or CO2 slush instead of a torch, but with the large thermal mass of lead bricks and
steel? See if there is a "liquified air" or other compressed gasses supplier in your area. You can readily buy liquid nitrogen, either
renting the Dewar's flask with it, or supplying your own thermos-type containers. It won't be
cheap, but if you literally pour a bucket of liquid nitrogen over the stuck bricks (using a clay dam or other to confine the liquid)and then wait for it to "boil off"...that thermal cycle should break any
corrosion there is between the two. Making sure the compartment has been ventilated, then go back in with a maul or sledge hammer and gently WHAP the bricks. A crowbar may not be necessary, depends on how stuck they are.
But lead bricks...any
heating can cause toxic vapors. If all else failed, you could literally torch them into liquid state and then clean off the last of them and the corrosion afterwards, but that's a very dangerous (long term and short term) way to do it.
So I'd vote for freezing them, with a generous amount if liquid nitrogen or other cryogenic gas, whatever is available to you.