What's needed to convert a big bumper Jetta front end to a small bumper Golf front end?
Golf Slam panel, Lower panel( if the jetta doesn't have one) suitable bumpers lights etc. Suitable skinny bumper spoiler at front either 16v or GL. Could be done in an afternoon with a socket set.
yep, slam panels and bumpers really are just bolt on and pretty easy to work with

just make sure that whilst removing the front bumper, the central bolt on each side is present, this bolt holds the front cross member to the chassis legs and stop the whole lot from falling out if you remove the bumper
you'll see what i mean if you look underneath at the chassis legs/crossmember