A 318 is one of those engines that you could live forever on just about any oil. When I drove a 318 daily back in the 1980s through early 2000s, I used Mobil 1 10w30 and it just kept going, and going, and going, and going. Still would go if I pulled the car out of storage, for that matter. The TBI version, like my carbureted version, doesn't have the issues that the later Magnum series had where a lower intake plenum leak could contribute to sludge and grit formation in the crankcase, either. When I did a timing chain on mine at well over 300,000 miles, it was very clean in there.
All in all, I see no reason to change what you're doing. I've never been a big Castrol fan and would probably use M1 5w30 Extended Protection or Pennzoil Platinum myself, but honestly the Castrol products are probably pretty much on a par with Mobil and Shell/Pennzoil for that application. Plus I don't know what oils are readily available to you. Same for filters, you could stick with Mopar or go with Wix, Baldwin, or Purolator if those are available in your area.