Needle time..

[OldBlackFocus]

Good evening, as my name suggests I am the owner of one of Henry`s creations. Its an aged vehicle but still more than capable of inducing an occasional grin. Well it was, it seems to have an injector problem.
Mk1 Focus `54 plate (so I guess a mark 1.5) 1.8 ZETEC not too many about in comparison with 1.6s and 2.0s. ANYWAY, I digress,
Are the injectors interchangeable across the engine range or does each one have a different injector designation?
Thank you in advance