From my general research IIRC there are TOS Japanese LD releases in boxset form that have digital audio but are hugely rare and very expensive.
Analog mono on LD is surpringly good but still technically below what you could get via VHS hifi or Beta.
My thought would be to use DVD mono if possible as it would be easy to find and likely is the source of the other BD mono tracks anyway.
Edit: I didn’t realize the DVDs are all 5.1.