B2 PCBs and components arrived a week ago, and it's now complete. B2 comprises TIMERB and CREGB and, with the lessons learnt in B1, everything worked beautifully on my first try.
TIMERB counting TIMERA underflows works, and I only need to determine it this is cycle accurate compared to an original 6526.
Meanwhile, design for SDR and ICR is mostly done. Hopefully, it will be built and tested before the end of year.