all injectors will tick, this is the valves in the injectors opening and closing, if yours are modified to be higher flowing than standard they are putting in more fuel so you probably have more of a tick. normal, but if its abnormally loud or annoying run some injector cleaner through the system. when using injector cleaner the best way for it to work is to take your car on a long trip down the highway. injectors out of new motors have better technology and would be quieter than older model ones. sometimes injectors are too gunked up and the cleaner is not enough to clean them, but try the cleaner from supercheap or repco as a quick easy fix.
any mitsubishi magna v6 injecter fits straight in and instead of having 2 squirt holes in each injecter in the standard holden ones, mitubishi ones have 3 and flow more fuel. ive noticed a power increase probably about the same as getting the v8 throttle body. although ive changed my fuel mixture and timing throguh the memcal.