Unless you made the bike into a raked out chopper, I wouldn't be concerned about the head tube breaking off your bike. If your frame can't handle a reasonably longer fork, it wasn't very strong in the first place.

I know you said to ignore handling, but putting a longer fork on will decrease head angle and increase trail. If you also reduce the rake of the fork, you will further increase the trail and aggravate any handling problems you created with the longer fork. You need to increase the rake of the fork to bring the trail number back to where it was.