My "personal opinion"? Go with reservoir shocks. They will be able to take a lot more heat in the long run. Their only downfall is that you have to have them serviced more than a "normal" Bilstein (or other monotube shock), but they still last a long time. But, if you've done your research and are satisfied, get the 6100's!
What type of terrain are you planning on hitting? Slow? Fast? If you're in the fast mode (and good for you!) the reservoirs will reduce shock fade by providing fresher oil through shock cycling. Shock fade really sucks!
I don't know of anyone who makes a "kit" for the rear hoop. All I can tell you is that if you do mount them through the bed you can just make a bent rail on each side of the bed (over the frame) and attach the two of them with a crossbar. If you have heim joints you can easily put the mounts on that crossbar! I have a friend who welded one for himself on his Toyota and it works great! Nothing too snazzy; it just works. The other option is to weld a cross bar from frame rail to frame rail. This is a lot better if you already have a body lift of 2" or more. If not it will be difficult to mount and service without pulling the bed off!
You had asked WeaZle about how to mount them -- straight up or at an angle? The best is to have them straight up and down, in a PERFECT WORLD. The reality is to have them at a slight angle will help you out, as the rear end never truly moves straight up and down. It should also help, mildy, with axle wrap if you mount them at an angle. A good fab shop should be able to make the hoops for you if you don't want to do it yourself, and if they are knowledgeable should be able to give a better idea of what you need based on how you wheel...
Coil sprung is a good way to go, and very tricky and expensive! Let us know your progress on it! I'd like to know!