split object into equal halves i've made a mistake - modeled a complex (consisting of a number of meshes) object without a mirror modifier.

and now i came to unwrapping and decided to use mirror modifier.
but stuck. i don't know how to split this object into halves, because tools i know (knife, edge loop, bisect) won't do it.

i was adviced to use boolean modifier first with a cube. it seems to work, but may be there is some simplier way?

EDIT: boolean worked only on somehow simple objects, but failed on something more complex.

here is the image:

it is perfectly symmetrical. it not always has edges in the middle, but i think it's not a problem (faces there are flat)?

here is the blend: http://www.pasteall.org/blend/43072
'Knife project' works well here :


Add a plane
Place one of its edges along the middle (at the exact center)
You may work in a ortho view and along the axis (here top ortho)
Stretch it so that it covers your mesh
Select your mesh (keeping the plane selected) and enter edit mode
Hit 'knife project' and make sure the option is 'cut through'
Select the half to remove and add the mirror modifier