I have just completed another little experiment and replaced all the 74xxx ICs in my newest Apple-1 build (lucky number 7) with LSTTL. The Schottky muxes I did leave alone. Power drain on the +5V rail went down from 1.4A to just 0.95A, which is good, so I can use a weaker TO-3 regulator rated for 1.5A (and able to do 2A max) and a smaller low profile heat sink. These weaker regulators also happen to have the cherished "golden" baseplate that appears to be unobtainium for the LM323K, but was spotted in some original Apple-1 (note that the stamp on the regulator always can be altered, but turning a "steel" baseplate into a "golden" baseplate is much more tricky).
This said, my question for which the search function on this forum did not yield results: I seem to remember that somebody did claim somewhere that in the Apple-1, the 74161 can't be substituted by 74LS161 because the former had a bug (or quirk) the Apple-1 allegedly needs to function properly, and the 74LS161 don't have that quirk/bug/feature and hence, would not work in the Apple-1.
But my Apple-1 seems to work with all the 74161 replaced by 74LS161 (from Texas Instruments, if that helps).
So what is wrong ? Is that hidden feature really there ? Can anyone enlighten me / give links to more info ?