There is an original conversion tag from CAL around the desk here somewhere.
I have had a few of these over the years. Every one is a little bit different and, to me, represents the DCRA shooter's preferences and aim towards excellence.
I have always had success by just modifying the original .303 extractors. By removing a little from the inside edge of the extractor, and allowing it to come inwards a bit more, reliable extraction and ejection of the spent cases results.
I was lucky in that I found a half dozen of the Sterling Enfield mags in a garbage can at the local milsurp yard, and managed to buy them for a whopping $10 each. These did not have the ejector on the mag lip, so it was crucial to get the regular 303 ejector screw just right. When using the PH5C sight unit, the screw often did not project quite far enough to do the job. I found that one of the screws issued for the no4T (#69 scope) bracket was just the right length to work with. I still have a few of these screws hanging around waiting for the next conversion.
My current DCRA rifle is an installation that was done on one of the mid 50s no4mk2 actions. Picked it up at the Calgary gunshow last year for $300....hard to go wrong at that price.