really deserves better than SRT 600, though. If grip shift, why not xray 800? (I know you stated it is what you had lying around; do you plan on upgrading that?)
PSA for those yet to discover - BMX linear brake cable (which is available in a myriad of colours ) can be used as gear outer too as it's linear not spiral wound like traditional brake outer (thicker than modern gear outer but use brake ferrules and you'll be fine).