What is the horse power benefits

LISTEN to GTX John!! He's been going very fast for 50 years, and still is.
If you want to stroke a 318, a 360 crank is NOT the way I would do it. For really high performance application, get a 4" all forged kit FOR a 318. For budget street use, cast crank kit with hyper pistons would be fine.
But if you expect a big horsepower boost, heads will have to be MUCH better than 318s, and a cam will have to match what you plan on doing with it..
With good heads,, decent cam 400+ hp should be easy.
No kiddin! He's da man!