Clan War challenge idea using current matchmaking system

With all the clans currently trying to match each other I think it's time for this feature. It however needs to be set up as to not allow any ♥♥♥♥♥ing of the current system. Looking for input as to how to do this, here is what I got so far.
1. You pick your lineup, same as we do now when we start a war.
2. Enter enemy clan tag you wish to challenge.
3. Enemy clan now has to match not only the lineup size, but also be within the current allowable matchmaking weight algorithm.
4. Enemy clan only has X amount of attempts at this and when its within the range for a match it's locked in. No 2nd chances to find a better lineup.
5. The clan war between the 2 clans will start the prep day when the 2 clans are next available. So you can't start another war until you finish the challenge war.

Thoughts, suggestions, ideas, etc.?