Are you sure it can be fitted to another alarm system?
I would check with a fitter, or Clifford but I suspect that they would say no and advise you to buy a whole unit.
IMHO I would buy a complete Cliffor unit and get that Blackjax as an extra as it my not be 100% compatible, the last thing you want it to be moving at high speed or on a twisty road and the thing cuts in as there is a problem or somthing.
If you do a search for "Bargin Clifford" I talk about my bad experince when it did cut in as I must have enetered the code wrong and the blown fuse that cut al power, ABS, steering, lights, hazards etc at 60+ mph on a busy twisty A road, it aint nice!
£500 well spent if you ask me!