Hitech,
The angle limits for pitching bombs is to protect the bomb bay, fuselage, props and engines from being hit. AAF placed limits on bomber and fighters wing angle and nose pitch during glide and dive bombing to protect from those strikes. I've noticed over the years you may have chosen not to model that.
When I was looking for the manuals I posted in here about flight restrictions, I ran into that clear explanation for the warning.
When you first introduced the B29, I ran into a player in the TA who would up it with 25% fuel and barrel roll it by climbing a few thousand feet, diving to the deck, and barrel rolling with the pull out from the deck. I have no clue if that was possible in real life, or if the airframe would survive it but, this is your unique universe.