Looking at the dimensions it's probably can't be done irregardless of how it's configured.
You don't mention the # of rounds on your 204 Ruger barrel. But you would be money ahead to sell your barrel and buy a new barrel chambered in 20P.I have a heavy stainless 24" AR barrel with flutes chambered in the 204 ruger, and would like Recommendations for a Smith to rechamber to the 20 Practical,