If you have to ask, it's too much.
To anyone who's even remotely serious, check ebay. There's an OBX twin turbo manifold on there almost all the time.
Raise the compression? no.
MHG? should be mandatory for any sort of reliability.
600cc injectors? doesn't have to unless he wants to make over 400rwhp.
reliability? a tt'd 7m can be a dd as long as you use good parts.
last i checked, a lot of people dd mkiv's, so the upkeep is really only in the initial build. if you do it right the first time, it'll be fine for years to come.
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