Basic swap question

Cant believe i couldnt find this on a Sticky or another thread, guess its so simple and im so dumb that it need not be asked. But here goes.

Im building an engine at the moment, while im still driving the car its going into. Now this engine is not the same block that my GT has, so.... what accessories do i need to have off the other car and engine that I cant use off the GT. Im sure that would probably depend on the block im putting im building right? well i'd rather not say because people always feel the need to tell me im ... well stupid. So generally speaking, if i cant find a donor car, what accessories do i have to order that would normally be incompatible?

Thanks for all your help Gents

P.S. Oh and one more thing, its an slightly older engine going into an 04.... if that helps

Yeah i figured sorry, im doing a teskid build, i plan on switching to coil on plug design to get rid of that problem, but im not sure about the rest, of what could be used from my GT and what cobra accessories im going to have to buy... Ouch pricey. Ive researched it alot, and i have a technical on how to drop a 99-01 Cobra to GT swap... it seems pretty simple, but i dont have a donor car, and since its older than my car i wasnt sure what else would change, other than bellhousing, the coil packs, and i think i heard something about IMRC delete since im using B heads. Other than that i was told i had to extend a few wires but it was supposed to be plug, play, then flash. Im not in any real hurry either, im not planning on putting the engine in until its just the way i want it, in about 6-8 months when my deployments over. The place i bought the block from said they'd mail me in all the front accessories from the engine for another 350$. They however failed to mention what they were haha.

Thanks again, this place is an awesome resource of knowledgable(sp?) people