I am no expert on your quandry, but logic must be applied. Your car "as is " is worth what? Add the cost of TT lump and ancilliaries, plus all the other gubbins needed to convert to Tiptronic. Do you need a new prop and diff with this set-up, probably likely (awaits confirmation)
Then, factor in potential labour costs, even if you are doing the work yourself, then imagine the scenario that would ensue when you eventually get it road-worthy, and need to inform your insurance company thatyou have changed your car, barring the shell, carpets and seats?
Imagine the scenario when you may need to sell the resultant project due to an unforeseen personal circumstances...............May be worth a third of what its cost you, not to mention the blood, sweat and tears.Forget it, sell your current motor, and buy what you ultimately desire, and save yourself some money, etc, etc.
Sorry to piss on your chips, but I am sure the majority on this forum will agree with me:)