Thank you for your comments. I understand your concerns but I believe they may be somewhat overstated. What you say is applicable if the bearings were used in a high-speed application like a wheel bearing etc.
In a no speed - low load (relatively speaking) as long as the surfaces of the bearings and the cup meet as designed you will get satisfactory performance from the bearing. The 30mm bearing rides less than 1mm higher in the cup of the 28mm bearing and is within the machined wear surface of the bearing cup and still deep inside the steering stem. I believe it will work safely in this application.
Failures in steering head bearings occur over time and I have never heard of a sudden catastrophic bearing failure. They are usually attributed to lack of lubrication and infiltration of dirt and water allowing the bearing to beat themselves to death. It is witnessed by sticky or notchey steering and that is when it gets un-fun or dangerous. Letting that go is really bad.
FWIW, I am an Industrial Engineer by education, worked in the power-transmission and industrial automation fields for too many years to talk about. And I too have been doing this type of work...for about 40 years. It is not ideal because you have to buy 2 bearings to make it work but it is easier than pressing out and turning down the stem.
Your installation looks great. Thanks for sharing the album.
Are you using a KTM forks, wheel and aftermarket oversize off-road brake kit? If so, what manufacturer did you go with and how well does it work for you?