Remove the wire between terminal 50 on ignition switch and terminal 50 on starter solenoid.
30: to constant 12V power source: battery+ or 30 amp fuse (12 awg wire)
87: to terminal 50 on starter solenoid (12 awg wire)
86: to terminal 50 on ignition switch (22-24 awg wire)
85: to ground (22-24 awg wire)
You can use heavier gauge wire on the 85/86 terminals if that's all you have, but they don't carry much current so it's unnecessary.
The dash location is fine, but their will be less voltage drop mounting the relay closer to the starter. In that case you can just connect the relay #30 directly to the large #30 lug on the starter solenoid instead of the battery or fusebox.