Ok so fitting a rear caliper kit to our GTA using the Mac#1 Kit, had to adapt a bit becuase were also using Ali rear bearing carriers. Best alignement of the disc in the caliper i can get is just about 1mm off dead centre, what are your thoughts?

That would worry me too much however the most import thing is that the calliper presents the rubbing surface of the pad pad as close as possible to square on to the disc surface if it doesn’t then you will get a spongy long pedal.

everything is square and with some faffing ive got it down to less than a mil difference between the 2 sides, im thinking that should be fine...what do you reckon?

If I understand you right you're saying the caliper and disc centerlines are +/- 1mm off?
That would mot bother me in the slightest. Discs and pads never wear perfectly evenly around the centerline and usually by more than +/- 1mm.

That assumes all components are in good working order of course.

A worn disc can present more than a mil offset, so I'd be fine with it. To be fair, once I start building my car I'd be well happy if I was only worrying about fractions of a millimetre!

If you think about it what your saying is when your pads are worn out 1 will still have a mm left so what

The disc offset won't matter to the caliper. Whether twin/multi piston or single piston "floating" type, the caliper will simply centre itself on the disc.

The only real issue would be that normally the caliper carrier slot is only just wide enough to fit the disc thickness, so any offset can have the disc fouling the carrier. If this isn't happening, you have no worries - near enough is good enough!

Cheers R

As said earlier nothing to worry about just ensure the gap on the widest side is sufficiently narrower than the thickness of the steel backing plate of the brake pad to give an adequate safety margin against a badly worn pad slipping through the gap between the calliper and disc.

Thanks for all the input, in my own mind i was happy with getting it that close, i could get it closer but it means machining up some spacers and stripping the whole lot off again which im loath to do, so once i get back from hols it will be onwards and upwards with the handbrake mech.