Have you done the finger test on the ICs to see if any/many get hot really quickly?
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Your best bet for electronic parts in Oz is rs components. Best part is they do free shipping with no minimum buy.
They have these:
74LS164 --> 74LS164
74161 --> 74LS161
CD4066 --> CD4066 or 74HCT4066
74LS253 --> 74HC253
74LS393 --> 74LS393
74LS04 --> 74LS04
74LS86 --> 74LS86
Hard to know if the substitutes will work properly though.
Like ForceFlow said, it could literally be every chip that's gone worst case.
Are you at least getting correct power-supply voltages?
Also try contacting user Skybeaux on AussiePinball or AussieArcade forums who is your local respected board repair guy.
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