If you think converting a MB to US standards is expensive wait until you try to convert a blond, LA arihead to a reasonable person. With the US balance of payment what it is we can really use all the cash you are willing to bring.
I converted a Euro 280slc and a BMW 3.0csi to US standard in 1983 and at that time it cost $4k a car. And that was in Texas, not Calif. When I lived in Perth, WA in 1977 In 11977 I converted a 1972 Land Rover stationwagon, that I had driven overland from the UK, to right hand drive. It wasn't fun but all the right hand drive parts were easily available there and my labor was free. Such will not be the case in LA. Junk parts may be availabel but unless you have a lot of spart time and another car you will have to farm out the job. this means labor rates of probably $75-90 an hour, plus, plus, plus.
Regardless of what you have done to and for your SL I would highly advise you to sell it or store it in Oz. Cars in the States are too cheap by half to mess with converting your MB. If your car survives the LA freeways it probably won't survive being stolen. If you just have to drive a SL look on
www.cartrader.com or the like and price a US model. Remember, once you convert the car not only is it just another SL in LA, but now it has a bodgie past and the VIN is probably not listed making it impossible to sell in needed.
Good luck.