I know the conversion is possible, I shot with a fellow using such a converted pistol - magazine. He didn't seem to have any problem with it, although the rim on the case does tend to curve the stack. To be honest, I haven't done any Dremelling on my magazines yet. I'm thinking about it; but I haven't shot much PPC lately.
I think the five round block is more related to Bullseye shooting which is done in five shot strings.
I sure like my 52. It shoots so good it makes me look good.