Following shall answer to those who have concern on swapping the calipers from OE to WK2.
A retrofit kit is you got what you got, as the primary concern is fitment, if it fits most likely the replaced caliper would work, may not be the best, but would be just fine.
If you want to know the WK2 caliper pistons it was listed here in our
caliper rebuild section.
WK2 (6 pot): 40/40/40mm, total area=75.4 cm^2
ST (Dual pot): 48/48mm. total area=72.38 cm^2
Not identical but close enough.
These modifications are very minor and once the locating pin is removed you will find the caliper (WK2) installation is actually easier than OE caliper as it's now more flexible than OE in posistioning.
Let's know if you have any other concerns or questions.
Members are advised that RB is a legitimated brake company and is not someone just trying to promote a product with just a screen name that you might know. Every kit/components are certified to be equal or better than OE or they will not be shipped.
Feel free to browse some of the high profile car communities, or GT350/GT500 in competition racing wthin Ford and learn more about us.