Is it possible to convert the LT1 2 bolt main into a 4 bolt main? What would one have to do in order for this to work?

 

You can buy a splayed 4-bolt conversion kit.... I have one from Pro-Gram. About $200 for the parts, if I recall correctly. Then the block needs to be machined and drilled/tapped to accept the caps, and the mains align bored.