If my memory is correct, they are wet liners sealed at the bottom with paper gaskets, and not a tight fit at all. I am sure that it was standard practice to put a couple of bolts and washers to hold the liners down before you turned the engine with the head off, otherwise they would pop up with the pistons and tear the bottom gaskets. That being the case,I dont think there is any real danger of the block cracking if they are removed, and in fact it would be a good idea to pull them out, god knows what those paper gaskets are like now!