A bit modern, but I mean, look at the car? :) RRP for a similar one is £136
Good old ebay! New for £49.95.

http://www.nfauto.co.uk/bulkhead_grommets.htm These will fit a 25-27mm hole and can be trimmed down to fit any size of the pipe up to 22mm. Perfect!
http://www.nfauto.co.uk/ provide all sorts of stuff! Well worth a look.
Should just be a sizing issue of the bore, or maybe no issue at all.
EDIT: Major whining on the Caterham Forum about the AP Caterham Kit and using it without a special master cylinder, the pistons are too big for a normal one...1/3rd more travel atleast...I think these AP need a (0.815 AP) or 0.875" master cylinder. You could try a Wilwood M/C but you'd to experiment I think if the pedal is not to required standard. Oddly though some folks say its ok :) Gotta love forums.
I know Caterham make stuff to go onto cars like the CSR260, which is a f'ing fast, these cars can in production spec lap tracks all day etc (well maybe their reliability is not that great but the brakes and wheels stay on!) I trust their judgement, as their kit is raced on by vast numbers of cars every weekend. Where Rally Designs Wilwood kit probably isn't.
Factor in buying some nice pads for the the wilwoods £80-10
Its about an even call it £575 with VAT for wilwood kits and pads with basic discs and £646 for Caterham bit less if they will ditch the brake lines...I got quite friendly with the bloke from Milwood MC in Stroud, so see whats cooking with him. The AP have integrale mount lugs which I prefer the look of, and same for some Wilwoods, but the kits are always radially mounted with an anodised mounting block...Something else to flex...
EDIT:
ALSO JUST FOUND ANOTHER SPITFIRE UPRIGHT brake kit!
http://www.jameswhiting.com/page9.html
http://angus.zenfolio.com/p434475895/
Alcon Calipers . More info when I dig some up. These use normal Caterham discs. Non vented and large pads. I read ALOT of favourable reporting on the Caterham Owners Club about this kit. Its got smaller pistons than the AP so there is no master cylinder sizing issues and long pedals due to large piston sizes. People seem to like these alot, especially with PAGID pads. Which are the current favoured pad of everyone it seems.No vented discs which does concern me, not 100% sure of the Caterhams are using GT6 sized disks of Spitfire ones, the brake caliper would suggest a GT6 disk? With the right pads they really shouldn't be that important provided the discs are good quality. Lighter too! Ponder that.
I am liking this Alcon lark, I like good quality components rather then just an overkill of lower quality stuff, ie massive crap disks and pads, when really high quality pads and disks will do a better job etc.. Factoring in the possible master cylinder experiments, the Caterham setup is getting expensive. You need to consider the piston sizes when buying calipers unless you like a 2" pedal of mush. If the Alcons can be used with a GT6 disk and some *gulp* £100+ Pagid pads (that last forever) I'd be tempted to give it a roll...
These megaexpensive pads will last 3-5x longer than Mintex or EBC. I read these Alcons were tested at Nurburgring in a Vauxhall engined Caterham and did the 24hr race with one set of really good pads...My car ate 2/3rds of a set of Mintex 1144 in 12laps of the Ring and about 40laps of Combe and a hand full of road miles...Thats about 3hrs track driving.
With alloy hubs, my 7075 wheel nuts, superlite alcon calipers and non-vented disks it might be 6kilos per side lighter in unpsrung mass than the normal GT6 setup! About half the mass!
Not a single gripe with these Alcons on the forum, bar someone moaning about fade with greenstuff pads, but thats hardly suprising, but need some further debate on it. My car is probably not that far off an SV caterham with all the trimmings in it.
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Also the clutch is a 1600 Capri plate I think. I will need to consider buying an uprated clutch plate of the same O/D to ensure it doesn't blow itself to bits. I am very light on clutches and don't to burn outs or 0-60 timing much if ever, but I'd rather nor find its inadequete for the shear power.
Saying this removing the engine is a DODDLE! The exhaust manifold, carbs, fair ilter, water system (complete), engine mounts all come out as one unit. No need to undo or remove anything bar water and electric connection and the main exhaust pipe...All the water system, ancillaries come out attached to the motor or engine mounts. Forward planning has its benefits.
I should get my 2nd cheque from adsense soon, the adverts are here for your benefit...Sooner they start paying the sooner I can buy a quaife box :)
Suppose I should be out enjoying the celebration of another wonderful New Year for the human-race...sound a bit boring to me!
Anyway after the massive house parties we used to have that went on for days or weeks (no comment), a beer in the pub seems a bit dull to be honest :)