The 16cm exhaust housing does not require any changes to be made to the exhaust system nor does it require that you make any adjustments to your injector pump.
The adjustments to the injector pump do not necessarily have to be made in combination with each other. You can back off the starwheel a bit to get some more low end fuel if you like. However, most of us usually like to make a few adjustments to tune things where we like them.
As far as the HX35 is concerned, there are a few variables here. If you have a non-intercooled truck, it will require some modifications to the intake system to get it to fit. It is a direct bolt on for the intercooled trucks. The HX35 will fit 12cm, 14cm, 16cm, 18. 5cm and 21cm housings. You can change just the center section / compressor assembly and use your existing exhaust housing or change the entire turbo. No modifications to the exhaust system or injector pump are required. (Except if you go with a wastegated exhaust housing, then the downpipe will have to be shortened a bit)
Cheers,
Sean