group A coil will give a bigger and stronger spark and will allow a larger plug gap to be used. most people suggest a 1.0 mm gap when running a group A. Think mine is running 0.9mm with no problems.
Burton power is where I got mine from however alot of tuning companies can supply one. Was recommended to relay mine to stop any high rev misfires.
Oh using denso irridium plugs at moment. Hope this helps.