Add separate grounding to subpanel, split ground/neutral

I have a 100amp subpanel in my attached garage that is currently a 3-wire feed without separate ground. The neutral and ground are bonded on the same bars (which I understand was OK when this house was built, but no longer current code). I'd like to add a grounding wire and separate the neutral/ground in the subpanel. Feed from main panel to subpanel (shown coming up from bottom of picture) is run through 1-1/4 conduit, #4 wire, about 60 feet distance.

My plan is:
- run separate #8...

Add separate grounding to subpanel, split ground/neutral