After accidentally buying a Lucas rear caliper for the Mk4 which turned out to be for a Mk5 I decided to get them to fit. In case you don't know the difference is mainly in the carrier, the caliper is slightly different but that's easily fixable. However the carrier won't fit the Mk4 without some modding. I measured the difference and it appears the carriers are identical except the Mk5 one sits approx 6mm nearer the disc, so if you could space the carrier out by that amount it's the same. I didn't fancy a lot of washers so I had some spacers made out of zinc/brass, they are 27mm diameter by 6mm thick with a 12mm bore.
Today I fitted the spacers to the carriers, I araldited the spacers to the carrier whilst they were clamped by a bolt so no chance of them moving, whilst they were clamped I shaped them so they look to be part of the carrier, when I paint the carrier later you should be hard pressed to see them.
Took a couple of pics of the spacers clamped to the carrier, I'll take a couple later when the carrier is painted.
I've had 20 spacers made so if anyone wants to buy them I'll be selling them for £2 a pair. You'll need to shape them yourself if you want the same look. It means the in future you can safely buy Lucas calipers off E-Bay knowing if they turn out to be Mk5 ones you can get them to fit without buying Mk4 carriers which are approx £35-40 each.
You can see the spacers being used on the bolts as the bolt was too long