Firstly

Cappy.
I grew up fishing on that river so I used to know it rather well. The river has undergone radical changes over the past years, but what remains the same and unaffected is the guidelines for Grunter and Leerie fishing. Obviously, the biggest question is do you have a boat or Kayak? Regardless, I'll tell you what I would do.
Leerie: Upriver of the N2 bridge is deeper water and you may have more success with lures up there than closer to the mouth. The biggest concern is the shallow water before you get to the bridge and caution must be used when navigating this river and beware rocks under the bridge. The easiest and most successful way to fish for Leerie if fishing from the bank in uncharted areas is to take your time. Starts at low tide and walk the bank that you are on and watch for tell tail Leerie chases and splashes as the tide comes in. Any sand bank or bank that has a drop off of any kind will always be a good spot, so have a look at low tide. Once you find that spot, you'll see the Leeries will come past there in waves. A group will pass and then 15-20min later another bunch will pass. You need to be patient and keep your eyes open. It does not matter whether you are in the Bitou or the Keurbooms, the principal remains the same. Once you see the 'boil' of a chase, cast just beyond the fish and retrieve past it. If the fish chases, DO NOT speed up your retrieve, keep it constant. I would also suggest you get some Predator Plugs or ordinary plugs (Not too big). StrikePro's are great, but I have had Leeries follow Strike Pros and Chug Buggs right to the boat and my son will throw a Plug and he will catch. So if they follow and don't take, maybe change to a plug. The other thing is give consideration to changing the treble hooks to single hooks. It causes less injury to the fish so that you can release it safely. Nothing worse than hooking a fish and the centre treble hooks the guy in the eye etc.
Grunter: If you fish for Grunter, Prawn is always best. If you are fishing from the bank, use 2-O or 3-O circle hooks. Put the hook through the prawn's second join in the tail so that when the prawn is in the water, it lies as it would naturally. Again, walk the bank and watch for signs of them feeding. The trick (and the beauty) of circle hooks is that you do not need to strike. The fish will hook itself. And once landed, the circle hook can easily be remove and the fish released quickly and safely. Any bank will have some Grunter passing by at some stage. If you are in a quiet part of the river, you will see them and you will get a good idea of where to fish for them.
Any river has it's good spots. The problem is that what is good today might not work tomorrow or the next day. Ask some local fishing shops what they recommend, but use your own initiative. Advice is just that....advice. It's not a guarantee and the sooner you see things for yourself the faster you will start catching. Fish very early morning and late afternoons. Watch the water and watch for fish feeding. If you are there for more than 3 days, there will be no reason why you cannot catch.
BTW - Any fishing store can change trebles to singles for you. Alcocks will do it, I am sure. You'll pay for the single hooks and if they don't use the inline hooks, they will use two split rings. (The double split ring method is MUCH cheaper than the rather pricey inline hooks) Also, you can buy a small split ring tool that opens up split rings and makes it easy if you want to do it yourself.