Use a hole saw, drill a pilot hole the same size as that on the hole saw then bingo......or if you have them a rotobroach is a really good way if you must have them on the roll bar as I would sooner see them fitted to the chassis.

:D

Mine are either too big or too small, besides the two way postage of one would probably be almost as expensive as an ebay El-Cheapo :D

where would it be mounted on the chassis to get the right belt heights for iva?

The top rail that runs along the top of the seat bulkhead is plenty high enough

Also use some form of lubricant as you drill it( WD40 very good and cheap).:)

Step drills are good too, i have one thats steps from 4mm to 28mm in 2mm increments and fits in a small chuck no problems

Admitedly they are designed for lighter work but i have used them on heavier stuff plenty of times with no problems as long as you use an appropriate drill speed

That's where I've put mine and works well with the eye harness mounts

can anyone post some pics of how they've done this? I'm having a hard time visualising how you guys have done this compared to the suggested method in the book?

No one able to post a pic?