You can either weld up your current center diff

OR

Buy a RWD center spool for around $500-800

OR

DCCD. Its not a RWD conversion, but it allows you to change the center diff split between front and rear and send up to 65% to the rear. Around $1500 usually for this conversion on a 5 speed.

OR

stop being a fag and go buy a nissan

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RS Liberty - Because WRX's are only good for parts...