It's not to hard of a job. I pulled my lights and harness out of a junk yard truck. I didnt use any silicone under the factory gasket and they have never leaked in 8 years.

I have put cab lights on prolly 5 OBS Fords and everyone of them had the factory plug for cab lights behind the passenger kick panel. Route the wires down the A-pillar no need to pull headliner just the trim piece over the windshield and A-pillar. These trucks have a double layer roof, I used a straightened out cloths hanger and fished the wires from the drivers side hole to the passenger side hole, then down the pillar.