I have a small concern about flash channel volume when using the newer style Omega plugs for the conversion. How much length do you lose by adding the vent liner to them?

At one time the Omega plug was not dished on the powder side like they are now. I think you can still buy a old style Omega plug from PA Machine. Those would even have enough length to make a tungsten carbide bushing plug. Not cheap but it is another option.