I believe all dashes have pre-molded "hole" for the clock. It's a circular depression in the molded rigid foam. Can be seen from the back. "Feel" around the circumference of the hole with your fingers from the front. Cut it out with an exacto knife.
Yes, you can install the clock without removing the dash. It will be a great opportunity to brush up on your swear words. You may even come up with some new ones. 😁
The original harness has three wires. Brown is for ground, red is hot (always on), gray is switch power for the clock light bulb.
This thumb nut is larger and designed with a generous chamfer for installing blind. https://www.thingiverse.com/thing:3293694