Not a ton. The bracket holds a sensor in place, and the standoff will be supporting a belt tensioner that's anchored in two other locations. In compression, we're probably talking low double-digit ft/lbs just to torque the assembly in place.
The OD of the spacer is basically the same OD as the cap screw head.
I did the same, and only found them for very small metric screws, or for lugnuts which are much larger and use a different taper.
That is what I would do. If you can start with a hex recess fastener that should give you a nice centering hole for the bore. Also, I would lop the tail end off after boring the hole. My 0.02
