I'm sure someone far more knowledgable will answer this concisely very soon, but for what it's worth here is my take on this...
Funnily enough I've been looking in to this conversion for my A2 project and, as per usual, have come up with many conflicting posts! Caliper wise I guess it all comes down to the bolt pattern of the caliper to hub/upright and at further thinking the offset that the caliper runs vs the hub & disk...
I have read that to run the LCR's on my A2 I'd need to use TT225 hubs only, however I am still not 100% on that information as people also state that if you're running the 288mm brakes, as per Golf & A3 1.8T & Leon Cupra you can just bolt the 312mm, TT225/S3, carriers straight on... that leads me to belive the carrier bolt pattern must be the same on the hubs between the Golf/A3 1.8t and the TT225/S3. Further more the LCR brembos are direct fit to the S3, so again, in theory, the LCR Brembos must use the same carrier bolt pattern as a Golf/A3 1.8T (or am I missing something?!!)
Where am I going with this you ask?!!
As luck would have it I have the stock 288mm set-up from my A4 kicking around and I also have an A3 1.8T donor car so I'd be more than happy to pop outside for you to see if the A4 caliper fits on to the A3 hub and over the A3's brake disc. Surely that will give a good indication as to whether LCR brakes fitting an A4 has mileage in it? Oh and that is with me guessing you're using the original B5 uprights and not the S4 ones?
I do admit though, unless you're getting a cracking deal, I must ask if it is worth all of the hassle? LCR brakes seem to command a huge sum of money for what they are in my opinion and then you'll have to find discs or re-drill the 323mm LCR discs to x112 stud pattern anyway. Surely you're getting close to hitting RS3 brembo prices by then? But that's another post entirely I guess!!
Anyway I hope this helps and sorry it is so long-winded!
Cheers. I'm already running a 312mm conversion using A6 carriers so was hoping the caliper bit would just bolt up. To be honest the brakes aren't bad so if this is loads of faff I'll skip it. Always worth asking when a good deal is offered.
The LCR brembos will bolt onto an standard B5 A4 upright as far as i know. The disks however wont fit at all, and cant be redrilled to suit as the offset is totally different.
I imagine a suitably sized disk can be found with a bit of research and a bit of tweaking. Perhaps the 330mm Merc disk for instance.
The LCR Brembos are sized such that the pistons are the equivalent of the original mk4 platform calipers. All MK4 stuff uses 54mm pistons, whereas the B5 uses 57mm. Thus the pistons in the LCR Brembos are a little smaller than you'd want for the A4.
Farmer: For your A2, theres a further complication. Most A2 models have an upright which has an integrated caliper carrier. Theres simply nowhere to bolt on a different caliper. You would need to find another PQ24 car which had 288mm brakes from the factory, and relieve it of its front knuckles, in order to have the mounting points that the 288/312/LCR brake systems require. I dont think you could use TT225 knuckles on a PQ24 car, they'd have to come from a Polo GTI or Fabia VRS etc.
So yes, it could be made to work, but i'm not sure its worth it, given the piston size issue and the premium price they sell for...
For my track car i'm sorting a conversion using the brembo calipers from a Megane 225/Clio 197. They are available for around £200ish, and have the right size pistons to work with the B5 master cylinder, and are radial mount so ideally suited for making some brackets.
Change your uprights to later A6 tdi alloy jobbies And YOU can fit the HP2 calipers and 320mm brake discs- dirt cheap and more than man enough for your car. If 320mm is not enough then swapping the carriers to b6 s4 will allow 345mm discs and massive choice of pads! 345mm are good to stop 344Bhp s4 coupled with 300 mm rear brakes and larger master cylinder !
Cheers mate but not getting into mucking about swapping uprights. The 312 conversion with ATE Super 2000 works pretty well and will do 8 or so hard laps at Bedford before they start to run out of bite.