Hi Tom
I have those very mushrooms fitted to my build at the moment & have found no issues.
Have a nice pair of Red anodised alloy ones to go on the build when it goes on the Road ( Thanks Kev
)
The pair currently on my build were CNC machined & were specifically designed for the Sierra front upright.
The drawings on this forum were kindly drawn up by my Nephew, a post graduate mechanical design engineer
I hope that this is of some help.