Based on my early Rabbit experience ATE/Ate looks reasonable as the original manufacturer. I've no proof that the Iltis is this way but would guess that both master and wheel cylinders might be the same manufacturer.
I did a google on "VW 183-611-019" and came to
http://www.iltis.co.uk/?paged=7 that suggests the master is similar/identical to an Audi 100, explains some of the dimensions and mentions rebuild kits. The last 6 of the part number are the same and the first three different. In VW speak, do the first three equate to vehicle type, i.e. is an Iltis a type 183? Does it help you?
For copper washers, good OEM or jobber washers (for CMP we use Malmberg as supplier) may be softer and seal better at lower banjo bolt torques than Princess Auto washers.
For the wire brush in the cylinder bores, I would be happier with a brush softer than the casting bore to reduce risk of damage. Brass brush?