I'm not sure what you've done before, so I'm going to be pretty broad and basic.
Can you reproduce the noise without load or is it only under load? If you can reproduce it w/o load it'* probably mechanical.. but if it'* only under load it has a higher chance of being electrical [more specifically what the ECU is seeing and what it'* calling for]. If the noise is consistant whether under load or not, try running a tank of plus through and see if that helps any. If it does, you can at least narrow it down to an ignition problem. If it doesn't, I would be leaning towards valvetrain [it could also be that the timing is so high that even 89 won't handle what the ECU is calling for, but on this engine I highly doubt that, and because if the timing is that high to begin with you wouldn't be hearing pinging, you'd probably be hearing detonation].
Fill me in on some more details and we can go from there.
'89 SSE - GX3 -190k, 155k on body - Back for another ride.