Stephen -
You're bringing back memories with your pics and questions! I have Rennspeed bumpers and had similar mounting issues. Yes it seems like the bumper is wider than SC flares. I wonder if it has something to do with Yellowbird having 1" wider flares than a SC?!!
I used the method in your first pic. Line up the ends on both sides as best you can. Drill a mount hole near the bumper end and bolt it to the fender, also bolt up the fender extension mount on the bottom of both ends. Then try and go around the bumper figuring out where to make mounting holes. The stock fender extension gaskets help with figuring out where to place the mounting holes.
You kind of have to split the differences on both sides to make it presentable.
It took me a few tries to get it to look similar on both sides.
