You'll need a 435 game cache to run the client. One is supplied in this repo, that one is loading 377 maps.
Once you have a cache, throw it into ~/.435cache/ or if you are on windows: C:/Users/<YOUR_USERNAME>/.435cache. The update server is currently disabled, so your server won't need one.
This client pairs well with RuneJS, a RuneScape game server written entirely in TypeScript for revision #435 of RuneScape.