I dont think its as simple as a one size fits all X=Y. You need to do a bit of work.

What sort of 4231? DMs or CMs? 3 wide AMs or narrow?

Are you the underdog or the favourite - what is the quality difference?

Which are his weakest and strongest players?

From this you can work out a plan...and then see if it works. Very rewarding if you get it right, much more so than getting an answer off the internet which may or may not work.