I drive a stock '68 Beetle, with original apron still in good shape.
I've used the 1 5/8" EMPI merged header (actually it's non-merged when you look at the crappy welding inside
) and have also run the 1 3/8" S&S header years ago. No modifications to the apron were required for any of these, except the EMPI, as the 1:00 flange point touched the bottom of the apron. Here's my current 1 3/4" Bugpack header with A1 Magnaflow turbo muffler...it just misses the bottom of the apron at the muffler flange.
The touched-up paint that you see in the photo is from the previous EMPI header hitting the back of the apron during engine install...stay away from EMPI headers...they are made in Taiwan or China and are poorly constructed). The Bugpack header, however, is a work of art: