I have a Halcyon plate that I use for very cold water drysuit diving. To make the plate heavier, I took about 10 pounds of old lead weights, melted them in a turkey frier, and poured them into the channel on my backplate. Took me about an hour or two to set up the plate and do the pour, and I came out with an 8 pound weight. The two together are about 14 pounds, which enables me to wear little to no weight with the drysuit.
It also lets me wear *just* the 6 pound weight with my wetsuit and be weighted very well. I might end up getting an Al plate sometime if I do any warm water diving.
Also, I'd at least think about the Oxycheq wing just for the possible cost savings, if that's an issue in Australia. Many people seem to prefer the Oxy over the Halcyon wings.
In any case, I'd stick with the Halcyon plate just to buy everything as a package, and do a lead pour or buy a weighted STA to decrease the lead on the weight belt. Trust me, doing a custom pour is very easy as long as you have a cheap stainless steel pot to sacrifice. I'm the least handy person there is, and I did it. I bought some thin 6" by 6" aluminum strips (used for gutters) and cut them to fit them into the camband slots, then blocked off the ends with plumber's putty to form the mold. I tossed the lead into the large stainless steel pot on the turkey frier, let it melt, skimmed off the gunk up top with a long spoon, then poured it into my plate. Went smashingly. It's hideous but it works. There are pics up at
http://www.jonnythan.com/scuba/