What size of front mount IC should I use on a 97 MK3 with a 1.9AAZ?
as big as you can friggen run. there is no such thing as too big.
i fitted a tdi intercooler of a mk3 but if you wanted, a sharan intercooler would fit in the front bumper if you cut out the slats giving it more cooler air than the usual wing mounted location. i also used stainless steel 2" piping allround. see my ad in the classifieds for some pics:
http://www.vwdiesel.net/forum/index.php?topic=20873.0Sal