Check to see if you have the horizontal bar installed (seems like it's 50/50). If so, you can wrap-around the bars instead of the brackets. If you don't have the horizontal bar or you need a bit more height, install the "ladder kit". If you snug the belts correctly and keep them spaced properly you should have no problem with them sliding off the HANS (I use the 2/3 Hybrid, which I find holds much better than the 3".) Also went to 2" seat belts, which fit lower on the pelvis.

Dont' recommend sternum strap as it's one more thing in an emergency that has to be tended to that emergency workers are not going to expect (or one more thing to undo if you need to get out of the car fast.)

The one thing I see "mis-mounted" often are the submarine belts (hopefully you went with six-point, not five). I seen them mounted like a five point (to a single center bolt) but they should be spaced apart so they wrap around the thighs rather than tight against the crotch (for obvious reasons.)

Posted a few photos that might be helpful when modifying a Butler to fit a HANS (and 2/3 hybrid Schroths)

http://www.flickr.com/photos/bobsrf/set ... 518897029/