Q:

What would an acceptable replacement be for a discontinued Motorola HCT174A?

I am trying to replace a Hex D Flip-Flop on an Amiga A4000 motherboard.  The original chip has the label
HCT174A
XAA346

I believe the datasheet describing this is the MC74HCT174A (though I can't find a reference to the XAA346), however, a BOM for the Amiga Motherboard lists
74HCT174, SOIC package
74HCT174, SM, EIAJ Package (as an subsititue)

When when I search Mouser.com I find 5 possible choices and the TI CD74HCT174M (datasheet) seems like the correct choice, is there anything to keep in mind when sourcing a replacement?

A:

74HCTxxx is a standard logic family (just as 74HCxxx, 74LSxxx, 74ALSxxx, etc.)
All manufacturers were supposed to abide to the same nomenclature, input and output logic levels, fan-in, fan-out, and timing. 
Parts within the same family are supposed to be manufacturer-independent. 
Furthermore, 74HCT parts were designed to interoperate with both 74HC and 74LS parts, to give more freedom to the designer. 

A:

What you are looking at is indeed a 74HCT174. This is a standard logic IC, so TI's version of the part (which you've found) should be perfectly acceptable. Hardware makers of the time would frequently substitute equivalent parts from different manufacturers -- notice the Philips 74HCT166 right above it, for instance.
The "XAA346" on the second line is a manufacturing code or lot number -- properly decoded, it can probably be used to determine when and where that specific IC was manufactured. You can safely ignore it.

