There is/was
an IEEE standard for the S-100 bus; why not hew to that,
regarding supply voltages?
But, . . .
would the standard, even early versions, such as presented by George
Morrow and Howard Fullme at the West Coast Computer Faire, really embody
the SPIRIT of S100 without at least a few non-standard signals?
That is why you have a 6100 on the S-100 bus and data lines D9,D10,D11,D12. :)