You'll have to tune the ECU for the MAF and injectors that are installed. Like esmth said it will trick the engine into thinking there is less load than there is.
I've got chips for LH that may or may not be a good fit for your car, there are other folks that sell canned tunes as well (KL...
I'll add that in addition to toe issues it looks like you have a pretty extreme scrub radius (imagine the distance between the center of the front tire tread and the axis of the strut mount and ball joint) which increases the lever arm on the bushings and control arms.
With the absolutely pathetic static compression on the B21FT you''d be stuck running the T cam if you want even adequate dynamic compression. You would stand to gain a lot by milling the head maybe 1mm.
The 531 with its slower, larger intake port will likely reduce fuel economy. Switching to a T cam and raising compression might help as well as chips but driving style will of course be the biggest factor.