There are as many ways of preparing a green crab for blackfish as there are anglers that fish for them. Most good tog anglers prefer to remove the top shell, but I usually dont. I also leave all of the legs dangling except for the two where hook comes in and goes out. Of course I will adjust my technique if I find that other methods are more productive, but I usually don't find this to be the case. By removing the top shell, I feel that you are inviting bergalls to clean out the meat and unless the blackfish really have their feedbag on, you may find yourself fishing with an empty shell. I am sure that you will hear other opinions about preparing green crabs and they all work. You just have to find the method that you feel the most confident with. Regarding rigs, I like a Gamakatsu 3/0 octopus hook, but I certainly have faith in the traditional Virginia style blackfish hooks that most anglers use. If I am on a wreck with a lot of BIG fish, I use just one hook to reduce the risk of hanging the wreck. Otherwise, I use a tandem hook rig or sometimes a high - low rig with the hooks about 12" - 14" apart. As far as bait, I'll take a green crab over a fiddler on most days.
Gamakatsu