3.31” Crankshafts

Are poly 318 crankshafts: are they interchangeable with LA- does that include any difficulties ?

Not all 273 cranks are forged correct?

Would a 1960’s forged 273 crank need much metal (Mallory) attached to the crankshaft if hypereutectic (lightweight) pistons and I beam aftermarket rods were used in a 318?

Would a 1960’s forged 318 crank need much metal (mallory) attached to the crankshaft if hypereutectic (lightweight) pistons and I beam aftermarket rods were used in a 340?

Am shopping, and I want to know all the options. Thanks