drop spindles and disc brk backing plates

[mole2000]

I just got finished installing one of my new mcgaughy's 2.5 drop spindles for disk brakes and was shocked as I thought of the next step: install the backing plates from a donor truck. There were no attachment points tapped! The bosses were there, but no hole at all. I had no idea that I would have to be drilling and tapping these. Is that correct or could there have been a manufacturing error? Has anyone encountered this and if so how did you solve it? How difficult is it going to be to drill and tap out these attachment points? Do I really need backing plates at all? Any advice is appreciated.
Thanks.