I ordered 4 Ford shock towers so I could do all my shocks, there is a great write up at this link and at the bottom of the link is the part number for the shock towers.
http://www.coloradok5.com/ranchoreview.shtml
The shock tower is about 15" long and you decide where you are going to mount it then you cut off the excess. I ordered mine online at one of the Ford discount part websites and paid about $15.00 per tower. (A little grinder work and the Ford logo will be gone.)
I will be installing mine shortly. I ordered the new Rancho RS9000x shocks, part number RS99036 which gives a shock that is 21.125" compressed, 36.125" extended with 15" of travel. I did have to order 4 extra metal bushing sleeves as each shock only came with one metal bushing sleeve. These shocks have 9 different settings and I have read some good things on them.