Quoting Richard Price: Quoting TomGaval:
Is it as simple as drilling the appropriate size hole in the rail, inserting a bung an TIG welding it in and then tapping it? [/pQuote
Yes, essentially, that's about it.
Quoting David Nelson: There are a few sprinters using HANS and we us a steel plate to take the bolt holes to the appropriate position.
For my own seating position, I was able to use one of the existing bosses, adding one new one to position the harness' correctly.
Height is also critical. I'm short, and sit low in the car, so my harnesses are actually bolted under the bulkhead top rail rather than over it. I've then cut slots in the bulkhead that they emerge through.
As Richard says sitting height is critical. I had Arch fit mine and, as I understand it, the shoulder to anchor point angle range for the straps is 0 to -20 degrees from the horizontal.
I was able to use the top of the bulkhead top chassis rail, with both new points placed symmetrically to the centre line of the seat, inboard (unequally) of the existing anchor points. The holes in the Tillet seat required significant enlargement so the straps did not foul.