Well theres a mk4 up in this part of the world with 19's and a 40mm drop, there doesnt appear to be any arch mods, but then there may have been some fettling/rolling that isnt visible..ill try and ask the guy..
Personally i would replace the entire suspension system, as you can fit the springs on but uprating it all in one hit means that the springs and shox are matched for better performance and setup....depends if you want a 40mm drop asap or whether you can do some research and see what there is in your price range
Cheers
Ows