Are you sure you bought the right vehicle for your needs? When it comes to modernising a Series everything is possible and most of its been done, but a lot has been a waste of time and for everyone trying to add something there someone trying to get it all off. You don't say what year, but if its close to historic be careful on the points or it will cost a lot more than the parts and labour. The general rule seems to be "major modification" does not include a TDI, but once you change the transmission, add synchro and full time 4WD plus CVs its a "yes" and that can be expensive. You can fit a Land Cruiser transmission, inc transfer case and axles, (its been done) but next thing you'll want to fit the Land cruiser body (its got comfy seats, a decent heater, a radio) the engine (its got more power), which brings me back to my first question, if you don't like the engine or transmission are sure you have the right vehicle?