When I got this X (which has now been sold) the tach and speedo didn't work due to rust behind the gauge cluster. Let's just say, that if I can install these gauges, anyone can. I did not take photos of the building of the cluster, but I do remember it was fairly easy.
I think I had to "trim" the plastic around the holes with a dremel as they were a bit too small of an opening. I used the existing wiring that already went to the cluster area, and if I remember right, there were only about 4-5 wires to hook up. The GPS speedo has a "block" like sensor/locator that has to be routed and put on the dash. The tach gets hooked up like normal in the engine bay. And I remember the instructions were plain and simple. The face of the gauge goes through the hole, then you spin the back locking on. What I can't remember, is if the plastic front face of the cluster fit back on, and I don't think it did. That would be, the long plastic piece that covers the gauges from dust, etc. I think the gauges stuck out a bit and wouldn't allow it to fit back on. I wasn't worried about this at the time, but I'm sure there might be a solution, I just never kept trying as the car had other issues I felt more important to get to.
I would say the only down side I remember, is the wiring for the gauges is tiny (18/20? gauge) which made it a bit hard to work with.
Not sure if Speedhut can do reverse tach, but it wouldn't surprise me if they could. I've seen some of their custom gauges on their web site, and they are pretty impressive.
Gerald
