honestly, it will cost you WAY more to get decent HP out of a 2.4L than a 2.8L. to raise compression in a 2.4, you'll be looking at custom pistons. you'd have to have block out anyway, so why go through the $$ and hassle if you can pick up an L28.
L28s are simple swaps; just pull your old engine and replace it onto the L28. if you get an F54 block with flat pistons (not all of them have them) and then throw an earlier head (E88 from your 240, or E31, N42) you can easily and cheaply get 10.5:1 compression ratio. if you get the N42 you already have bigger valves, so no headwork needed. invest in a cam kit for around ~600, get a header and exhause and you're shining.