Possibly posted before but want to make sure it is known.
This should be a relatively simple process.
The Wilwood aluminum hat used on the 2011+ Fiesta, includes our ST, is part number 170-11902
It has the proper bore size for our hubs which they call Center Reg, 3.06"
All rotors are hub centric, stock, aluminum hats, etc which is good news.
We can use any 4x100 or other bolt pattern hat with the right center register, rotor bolt pattern 8x7.00, and then just find the one with the right offset to line the rotor up with the stock caliper.
If the offset is very close the stock calipers can be moved a bit with shims, if to far off then the hats can be milled to the right thickness, I had this done on my rear DIY 4 piston setup and it works just fine.
Since new caliper mounts would be required the proper offset can be machined right in so picking hats becomes easier and they should not need to be milled to fit.
All we have to do then is turn the hat 90 degrees and drill new holes in the 4x108 pattern or use as is if doing a 4x100 conversion. This can be done on a drill press or even a hand drill, just law a stock rotor on the new hat turned 90 degrees, line up, mark the centers, drill new holes. Best to round over or angle the edges to relieve any stress risers, I used a step drill which makes drill the hole and cleaning up the edges very easy.
(Note) put some blue tape over the hat surface first as the shavings can scratch the hat paint.)
There are 11", 11.75 and 12.19" GT rotors and some very low cost good rotors as well.
(STAY AWAY from drilled rotors, slotted are good, drilled not so)
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If I can get some measurements of the stock rotor hat height and rotor thickness I will look up the closest fitting rotor hat to help out, I have put together a number of DIY brake kits or modded kits offered using WW parts a number of times.
Rick