"Cured" rock normally means that the large, obvious dead organisms in/on the rock have largely decomposed away, but there is plenty of nastiness that can and will still be generated by cured rock. It takes months in a normal tank (i.e., with lighting, flow, filtration, etc.) for cured rock to mature to the point that it should be safe to introduce to an established tank. Cured really means 'no longer noticably rancid' and curing typically takes a month or so. Mature rock has functional microbial communities, established, growing coralline algae (if exposed to light, of course) and good filtration potential. There's really no substituting for the time it takes to turn "cured" rock into mature rock, which is several months of good tank conditions.
I've seen people crash their tanks several times before by adding cured rock (even relatively modest amounts) to an established tank. If it were me, I'd either stay with the 50 lbs you have (which is plenty IMHO) or set up an inexpensive tank (saltwater, strong flow, a heater and light is sufficient) to allow the rock to mature for a couple of months before introducing it, and then do so slowly, e.g., not more than 10 lbs per week. If you're intending to have a reef tank though, I'd stick with the 50 lbs you have, as I said. People very often put too much rock in reef tanks in the beginning and a year or two or three later are kicking themselves because as the corals grow the tank begins to utterly choke itself. Providing adequate water flow throughout the tank, for instance, can be nearly impossible in packed tanks.
cj