We all know that manufacturer's use products or different 'families' of engine parts, and they put them together to what we call an engine that we see under our bonnets, thing is though with a lil searching you'll can find that your parts are completely interchangable with other parts of the same family, so instead of going for custom headers or injectors use the internet to find out which family of engines parts does your engine consist of, this way you can make cost effective changes without worrying about compatibility. you can make minor changes(intake manifold/exhaust manifold), to head swaps, and tranny swaps..! in some cases you can swap a complete engine and use your original engine mounts. The nice thing about going this route is that there always going to be spares available and you don't need to be worried about 'custom' parts, however, be warned when you do plan something like this, go online and read forums about what you are planning to do and what you can accomplish realistically. Contact people on these forums, and exchange notes about the kind of problems they encountered. In short..garner as much information as you can.