Yes, that fitting will do the ninety. Should be something like that available local in nylon, etc. at any hardware.
But then the thought on getting the tubing straight might raise a couple questions also as the fitting does really cut the flow as you can see the inside diameter does go from 5/8 without fitting to somewhat close to 3/8 due to the fitting material. So that leaves me hoping a gentle curve could be made rather than straight tubing with fittings to make the corners. Part of the trouble is the change of direction and gentle curves work much better than sharp but the fitting itself is the major factor, so anything you could see to avoid that would help a lot. I think of water flow in tubing as something like traffic on a highway. Gentle curves slow you down slightly, sharp curves a lot more but closing a lane, like adding a fitting, can really throw things into a mess!!
But then, I'm also not the one trying to get it working in whatever space you have and you may be totally correct in ignoring my complaints!!