From NG to ABY

so times a question to all have to bring before me soon n s2 which also has more kilometers on it what if one completely overhauled the engine before the conversion? new bearings let everything regrind covert parts renew etc. what would the ca cost and to the conversion how much must one change? brake system is clear, I have to take over the axle also from the aby or ranges the from the ng? and which gearbox should one drive because it is a cabrio, some swear on the 6 gear from the 2.5 tdi some on there s 5 course of 2.8 gasoline. want to hear your opinion about it