from what i understand ,and have seen/heard is:the "later " 1.9 engine differs from the "old" 1.6 engine in cyl block heightby 5/8 of an inch(approx 16mm)and i read that in an old parts place catalog,cause they mentioned that if you used the same exhaust,and swapped to a 1.9 from a 1.6...you probably will have to lengthen the d/p by 5/8 of an inch,so it doesnt hit the "transmission tunnel"some vehicles may have hood clearance issues with a turbo pumpmy 91 jetta 2 door with a 1.9 block /1.6 head has a "altitude compensation" type pump(read turbo/lda, but its a na engine),,,,and it just rubs on the underhood insulation+makes a small impression on it
...BTW your Bieber avatar is awesome.-Malone