That's a pretty standard centrifugal oil filer design for the early Honda twins.
Once the snap ring is out, you can thread a long M6 screw into the inner half of the centrifugal filter to help pull it out. A 40 year old o-ring will be fighting you the whole way. Coming up with the special four-fingered tool to remove the filter nut from the crank will be the hard part. There should be a locking washer staked in place under the nut that will have to be flattened before the nut will come off.