the apk wont match up to a 20vt head but you can use the newer fsi engine bottom end with crank and rods but not pistons, so you would have to get bigger pistons. or you could rebore your current 1.8t to a 2.0 and use a fsi crank on that.
but tbh the 16v head flows better than the 20v head anyway. so you might as well do a 2.0T 16v engine swap which in my opinon is easier and more cost effective.