A quick question. Back in the day when 74LS was the primary logic family used for microcomputers, the output of 74 bipolar TTL logic typically sinks current much more than it sources (for example can sink 2-3 mA whereas it might only be able to source 0.5 mA). It seems that a lot of manufacturers are using HCT thresholded logic for many inputs as these are compatible with 3.3 and 5 volt logic thresholds for input and output, where the typical low threshold is 0.8 V and high threshold is 2.0 V. This is similar to NMOS, however, as far as I know there are no more NMOS process chips made. The principal difference I am aware of with HCT-like logic is that sinking and sourcing currents both tend to be quite high, 20 mA or more, and the high output threshold can typically be pulled up close to the positive rail at 5 V, whereas typical TTL might achieve only 3.5 to 4 V.
Can HCT logic be substituted and will its greater source and sink capacity at the output and/or its operation closer to the output rails be a problem when placed in circuit with older TTL chips?