The racket could be a number of things. First get a timing light and dwell meter to see what's happening with the ignition. Check to see if it dances around, or jumps back when you let off the accelerator (timing and/or dwell).
It can be the advance plate below the cam/breaker plate in the distributor. This loosens up at the swege. Check shaft play on the cam lobes.
**Get an Allison/Crand Cams breakerless electronic ignition.
Also if you've elliminated distributor as a problem and the timing shows a skip or jump especially when letting off the accelerator, you may need a new set of timig gears.
If the timing and ignition is good and you find the chatter is down low in the engine, you could have bad lifters. Take the valve cover off, remove the rocker assembly and lift out the lifters. If they are hard to extract or cannot come out the top of the bore, that's your problem. The solution is dropping the bottom end of the motor and removing the cam if the bottoms of the lifters are badly peanned from high rpm pounding.
Don't spend $$'s until you fix everything.
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'89 245 sportwagon, destroyed by hit & run driver, RIP. '04 V70 2.5 T Sportwagon, 12k mi and '91 245 5-speed, 209k mi, replaced the '89