If you are refering to the standard sort of ignition components (ie: coil, etc...) then just find a place up and away from direct engine heat (ie: exhaust manifolds, ec...). If you are talking about their upgrade modules (ie: MSD-6A, etc...) the same applies. Generally they give you a pretty long wire harness which will let you install it just about anywhere. Inner fender wells are a fairly good location. I'm planning to mount mine forward of the battery. One thing to keep in mind... If your Jeep has a computer - it is extremey important that you keep the main harness/power feeder away from your Jeeps wire harness and/or shield it. It will interfere with your Jeeps computer.
Good luck with your install. I haven't installed mine yet, but I'm looking forward to seeing what benefits it will provide.
CJ8 - Longer Is Better...