They are angled in an effort to keep the pickups tops aligned in parallel with the strings, instead of the body. The neck angle on a typical Gibson SG and LP sets the strings on a different plane from the top of the body…the space gets larger as you go from the end of the fretboard, towards the bridge. This is a common issue with the large pickguard SG models with their pickups directly mounted to the pickguard…the pickups are (often) not parallel to the strings…they are more parallel to the body top.
I have no experience with these, but I found them by searching Amazon for, “Flat Bottom Humbucker Pickup Mounting Ring”
The rings both of you have found are metric size. Most, 95%, rings you'll find on eBay, Amazon, etc, are metric and will not fit a guitar with Imperial measurements, like Gibson. Look closely at the width of the ends of those rings, the are wider than the ones found on Gibson. Screw holes will not align.
My Burny is a vintage MIJ. No Burnys were made in the US. Now they make all of them in China, so you have to be careful if you want a MIJ. I have a mm ruler arriving today so I can measure. But it looks like I have the highest made. So I'm going to order a thinner one. Both the ring and the pickup come up too high. Even if the pickup was flush, it would still be too high. That was my real question was what thickness was too high? Did I need rings that were both the same thickness, or are they supposed to be sloped? If I can find one that is still sloped but not too high, I'd be ok.
Then you should be able to find something once you take accurate measurements of what you have. I found a set that has a 2mm slope to them, with flat bottoms. Burny put out some really nice SG models. Some of the older MIJ guitars are super-well-made, but may have been “modified” over their lifespan…perhaps that’s the case here.
