I know you've asked NUTS RuS, but since I got a notification of post....

FRST - 239x20x43

2wd Cos - 283x24x55

(4wd Cos - 283x24x35)

Are your Wilwood callipers lug or radial mounting. If they are mounted using radial bolts into adaptors, they could have been drilled by whoever made up the kit to suit whatever offset chosen, as long as there is clearance from the knuckle and wheel.

If they are one-piece discs, its likely they are a standard size offset, and you have a wide choice of disc suppliers to choose from.

Martin