If you already researched this entry route sorry to duplicate, but just for the sake of clarity, you get an ILE visa endorsement (Indefinite Leave to Enter) only if, at the time you apply, you have lived outside the UK for four years with your sponsor and have passed the KOL (Life in UK Test). Otherwise, without the KOL certificate, you get a standard 27 month limited leave to enter endorsement but with an additional endorsement that permits you to apply for ILR (Indefinite Leave to Remain) at any time after you have passed the Life in UK Test rather than waiting the mandatory two years that is usually required.
You can only take the Life in UK Test in the UK. I'm only guessing that your wife has not previously taken it.
Provision of evidence that you were actually living together during the past 4 years, follows the usual stuff really. Utility bills, Bank statements etc etc spread over the duration and covering both of you.
Just as an aside and for your added information, the UKBA have recently shown their intention to remove the '4 year rule' if the proposed changes to the Immigration Rules are passed, so they're obviously not fans of this as it stands. They certainly believe too many applicants use the 4 year concession to gain quick access to ILR, set up a business in the UK and continue to remain resident in the home country as it's an easier and cheaper option to applying for an Entrepreneur visa or work permit.
Not that I'm suggesting that this applies to your case, but is simply an observation to show just how closely applications under the '4 year rule' may be scrutinised.
The new consultation on immigration runs until April 2012 when any changes will be implemented.
I'm sure you'll have no issues but forewarned is forearmed ....
Good luck
