Rear disc brakes

Can anyone tell me which wilwood rear brake kit is a bolt on kit? So for example if I had b body rear brake setup and wanted to put a wilwood setup on it what brake gap do I need? Is it 2.36 or is it the 2.5 brake gap? I have them on my car and can't recall which offset I have, I think it's 2.36. I'm asking for a friend who is looking to do the upgrade. Thanks in advance.