Hey "Sheep"
I'm new to the site, just saw your post. I have a set of these skis for my C170. I bought them for 8K in 2002 from a guy in Northern Minnesota. They are in pretty good shape, and I think they are worth the money. I'm based at an airport, so they are especially handy when you need to change back and forth alot.
1. WipAire, in St. Paul sells their hydraulic skis for about 18K for the C170.
2. The data plates are located at the very tail end of each ski where the tab for the cable attaches to the tail.
3. The resovoir for the hydraulic system with all the lines, connectors, etc are not shown...do you have them also? I did not get them with my skis and had to have them built which cost me another $1500 or so.
4. Axels are extra.
5. Many skis also have a Teflon or plastic sheet to cover the bottom surface which can be replaced as needed.
6. I had my pump mounted on the floor behind the fuel selector with the handle coming forward between the seats. This is much easier to use than in the passenger floorboard where you have to reach a long way to get to the pump. Pumping does require a fair amount of strength so its good to have the handle near your hip for leverage.
Not sure from your post whether you are selling or thinking of buying. Hope this helps. There are pros and cons for skis, but even though the hydraulics are expensive, I wouldn't ski fly nearly as much if I had to cart the a/c to the grass and cart it back to the hanger every time. It's nice to be able to change your plans along the way when you have the option of snow or runway.
My 2 cents

Good luck.
Odie