I agree with the above, it is better to buy a 20vt golf to begin with than to convert unless you plan to rebuild the engine. For one, there are many advertised 'engine conversion packages' for sale now and not just on eBay, theres no guarantee the engine is as advertised, if one was to install an engine that was advertised as having 48000 miles only to find it shows 110000 miles on the clock after all that work of doing the conversion there's few who would take it all back out again, strap it to a pallet and arrange for pallet line to collect it. This is a very real scenario and it has actually happened to myself before but the engine was intended for rebuild from the very start so wasnt so much an issue.
Although no one is saying not to do the conversion we are advising against it or to approach with caution and extra budget because of all the headache and possible problems. There are a whole host of other things that you should consider not least the possibility of getting a non runner, an engine with mechanical problems, work valve stem seals? Piston oil or compression rings, bearing issues, seized tappets or just dead, all entirely possible when you consider the 20vt engine from its infancy is now well over 10 years old! Buying a 20vt golf means you can test drive it for more than just a few minutes to make sure everything is good. Today you can pick up a 20vt golf for not much, so you really have to ask yourself if it's really worth it.