When doing patches for body work, butt weld joints are hard to fit up and inherently weak because in order to blend everything smoothly you have to grind the weld and by the time you’ve got it smooth typically you’ve ground away most of the weld! For this reason an overlap joint is nicer to work with, it allows some misalignment of the patch and allows you to put down more weld, and a hotter weld without blowing a hole through. The obvious issue is that in order for an overlap joint to sit flush there needs to be a step in the material for the patch to sit in. After looking online, there are some tools you can buy to help you achieve this... or you can just use some scrap steel and copy them...

A pair of vise grips, a piece of scrap flat bar with a step machined in it and a few tack welds and you’ve got yourself a cheap tool to crimp a step for an overlap joint. With a good line, a little bit of muscle and some patience you can crimp a pretty straight edge. Here’s a picture of the rocker on my E21 that I did last night...