This may be a completely silly question....is the difference in twist a problem?
Both cartridges can use the same twist rate, and if you want to use the 95 Partition then you'll need a 1:10" minimum. The .244 Remington (predecessor to the 6mm Remington) used a 1:12" twist and the longer 6mm bullets were marginally stable.
You'll have to set the barrel back quite a bit to clean up the chamber, this is not a "one thread" job. The 6mm-.284 is not a good candidate for a pure rechamber since at least part of the original throat of the .243 will still be there. I'd set it back ~4.5 threads if it were me. The half-thread part puts the barrel stamping under the forearm - a nice custom touch that costs nothing.
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