What is the horse power benefits

The 360 has a much bigger Main bearing size!
As I recall it is 2.81
The 318/340/273 has a much smaller Main Bearing size.
As I recall 2.50

You can buy longer stroke cranks with the 2.50 Main size.

A 4 inch would get you 391 CI as I recall.

The 408 converted 360 is a good combo!

The main caps are weaker and smalller on the 318 and we have
broken several when the HP gets close to 500HP or more.