My memory is old and failing but I don't think we machined much off the hubs at all.
We have abused this conversion on the track and doing club stuff for 5 years and it has been great.
I would not hesitate in doing this conversion again.
Cheers
Bob

"All tyre/wheel forces are transmitted through the wheel stubs to the hub and therefore to the suspension"

Sorry, but thats not correct. The studs only clamp the wheel to the hub sandwiching the rotor hat. The load (shear) is transmitted via the clamped surface faces only. Correctly assembled and installed there is only tensile load on the studs.
The hub OD should be turned and chamfered to allow it to fit into the rotor hat. The as cast "cone" on the outer part of the hub should be turned to spigot the rotor hat ID to the hub.
This is a robust conversion based on sound engineering priciples.

Ive seen the conversion done on 120y struts and with drum hubs but never on stock 1200 disk hubs.
There must be something different in there measurement.
Saw anges set up on 120y struts and hubs. Heaps of meat left on them

true about the wheel studs, but the point i was making hinges on taking 5mm out of the rotor, and is mute if it only requires 1mm. by the responses here it sounds like the typical conversion requires 1mm, and i probably have a mis-match in parts some how

[edit] changed thread title due to the above

the disc id (where it sits over the hub) is rough casting isn't it, so i can not see how this could be used to spigot the rotor?

ddiesel is right, next time you have a rotor in your hand you'll see that while you could just
machine the "cone" of the hub enough to accept the rotor, if you leave a chamfer on the base of the
"cone" it will spigot the center bore of the rotor locating it nicely rather than just leaving
that job up to the wheel studs.

the o.d of the hub also needs machining but again that is very minimal

if i still had the ute i'd take some pics and it would be much easier to explain (pics say 1000 words)

Well Rc has the disks I got of you Ange the 250mm s13 ones and I got a set of 120y Aussie struts off of Alistair, so Michael has the hubs from Aussie 120y and s13 ca disks and are having these issues, I have drum struts here ill measure and also sr20 s13 disks and see how much they differ

230mm S13 rotors? In Japan S13 came in 250, and 280mm versions and Europe also had a 257mm version.

Depending on the year, SR-powered S13 used 250 or 280mm rotors.

Sorry dd yeah I have both sets

I took 5mm off mine. Never looked back.
Mine isn't actually certified either. (Nor the supercharger lol)
I just go see mates to get my 6 monthly warrant of fitness inspection. (And pray I never get rolled by a cop who knows about cars/don't go out making a nuisence of myself/hanging out where the constabulary go looking for trouble)

I used early 120y struts, and didnt have to take much meat off the OD of the hub at all.
Just quickly turned them down on the lathe to mate with the rotors.
Im a big fan of this upgrade, although I do feel that the wheel bearings in these smaller struts, are insufficient for racing purposes.