It's entirely possible to use a 126mm OLN frame with a 120mm wheel. Just bend it a bit to get the wheel in or cold set it (check Sheldon) for a more permanent solution.
chainline is dependent on the distance from the cog to the centreline of the bike so assuming your rear end isn't off centre somehow, it's more a function of crankset and rear hub choices.
It's entirely possible to use a 126mm OLN frame with a 120mm wheel. Just bend it a bit to get the wheel in or cold set it (check Sheldon) for a more permanent solution.
chainline is dependent on the distance from the cog to the centreline of the bike so assuming your rear end isn't off centre somehow, it's more a function of crankset and rear hub choices.