This question has been done to death, discussed at lemgth, then bisected the perpendicular, to come to the same conclusion..............
a money pit which will take ages to do properly, to get, at best, stock TT hp. There are a couple of mad money builds on supraforums, but the concensus on here is forget it.
Best route is a TT conversion, done in a few days, with a TT autobox, around £2600 fitted and warranted.
Probably not what you want to hear, but imo, the only sensible way of upping an NA's performance for relatively little outlay. What about selling, then buying a TT?