So there are four things here:
- For the crystal oscillator, any different technology 74xxx02 chip will likely require changes to the resistors, as the different technologies all have different analogue characteristics (including different input and output stages),
- The oscillator is running at a fairly high frequency (this type of oscillator gets more tricky to get to be reliable as the wanted oscillator frequency is increased),
- The 6560 appears to need rail to rail signals on its clock input pins. So forget using 74LS02 or other types with similar outputs, as they cannot drive their outputs high enough,
- The two clock signals can’t overlap.
Oh, and it’s not normally recommended to pick up a signal from the middle of this type of oscillator. Best practice is to feed through another gate to help sharpen up the signal. Remember, the oscillator is operating in a quasi analogue mode, the signals may not be at normal (valid) logic levels.
I’m not surprised that Commodore had trouble with this design. That’s quite a list of requirements for one chip...
It would have been easier with trying replacements if they had kept the split between the oscillator function and the drive to the 6560 between different chips on all versions so that we could better match the requirements.
Certainly modern 74 series CMOS chips outputs should have little problem producing a rail to rail output suitable for the 6560. But will need the resistors in the oscillator changing so that the oscillation is at the correct frequency and start up and running is reliable.
Pull-up resistors help a little, but keep in mind at that frequency, their value has to be be low. Otherwise the time that they take to charge up the stray and input stage capacitance will be too long. At the same time, the value can’t be so low that the output stage can’t drive the line low enough, and fast enough...
Definitely use of a good two channel ‘scope is strongly recommended here, so that you can see what’s working and what’s not.
Mark