Yes, the rack mount can be a bit tricky with the variety of different styles out there. Some have very thin sheet metal "tangs" for mounting nothing more than a reflector, and I've seen these stress fracture and break under a heavier dynamic load, but I actually did make a nice Tubus-style adapter with the 50mm and 80mm spacing that worked really well. I just ended up not having a lot of call for it, and didn't make any more after the initial batch, although I may try to build some more in the next machine shop run. Turns out with creative use of the spacer material, most racks can use an approach like this: