Some engines rely on the lubricating effect of petrol on the valve seats, and need a modification to the cylinder heads. Depending on engine type, this could be a milling operation on the valve seats, or replacement of the seats and valves.
You'll need to know the exact engine type, to find out whether a head modification is necessary. A quick search shows it's probably the LS3. Holden used the LS3 in a factory LPG conversion. I've no idea what modifications they made though.
Performance depends on the LPG system used. Old-style LPG systems often resulted in a reduction in power. Modern LPI can get the same power level as petrol.
For completeness' sake: some engines can't be run on LPG. Recent engines from Ford and the VAG TSI are examples where LPG conversion companies have run tests but were unable to build a reliable system.