advice on replacing 1600driver bottom end with either 1.8 or 2.0

[sellers]

basically i want my driver to go zoom instead of chug


im after either a 2.0ltr or 1.8ltr bottom end to put on it from a passat or simular, had anyone done this? and how hard is it to do?
which one would be the best to get? i have heard mixed things about them?

[dubslug]

hey on my old 1600 hundred driver i had
1600 bottom end
1800 head
1800 gti cam
1800 gti manifold and exhaust
1800 webber carb
k&n panel filter
with all this the old driver wasnt to far off keeping with 1800 8vgti so im guessing if u had a larger block it would have increased the power even more??
im just abt to do the 2.0 conversion on the 8v gti so will let u know how it goes