Our lad just drilled his CB350F disc, using an old BMW Airhead disc as a drill guide.
Clamped the BMW disc on top of the Honda disc with two G-clamps, then drilled two holes opposite each other, did away with the clamps and used two 6mm bolts to hold the two discs firmly together while drilling the other 120 or so holes.
Came up looking a treat, as you can see. Used a countersinking bit to do the chamfers.
The BMW disc is exactly the same diameter as the CB350F's so holes were perfectly located regarding both inner and outer edges of the disc.
BMW disc was the same on R75 through to R100 models, 1970s and most of the 80s and were factory drilled.