The real figures on Dox block floor system are somewhat local. There were also some local variations and strengths available.
Try to contact local precast hollow floor plank (Spancrete, Spandeck, etc.)manufacturers. They were frequently involved in the product and may have even sold them prior to about 1965. They may have been shipped from 400 miles away.
I have seen the old design tables that a precaster friend had in his files, so I know they existed.
The product and similar ones are still used today internationally, but it is refined considerably.
I know of a retail store that was built in about 1960 that was made using bowstring(I think) trusses 16" wide made from block. - About 50' span, so they could do some surprising things then with good engineering.
Dick