Single to dual master
Adding a restrictor valve to the rear for front disc is an option . I just never use them.
With modern wheel-cylinder kits having the cup-spreaders in them, that residual valve is more or less redundant.
OP;
make sure your port to the front system, does NOT have a residual valve in it, else the front brake pads may be dragging all the time.
and, the disc-side gets plumbed to the larger reservoir.
The front side of that Combination valve is just a splitter.
The rear side has a hold-back valve in it to delay the rear brakes.
In-between the two is a safety switch, to turn the dash-lite on if one side or the other goes down.
Don't forget to "bench-bleed" the master, before you attach the brake lines. You must get the air out of the master, else you will Not get a hard pedal.