I'm willing to bet that while you were messing with the guage cluster you managed to ground a wire that runs to the tach. This wire gets a signal from the ignition system which in turn tells the tach how many revs to show. If this wire (gray most years) or other wires in the tach shorted somewhere, you'll have problems, though I don't know if it should be bad enough to have caused your ignition system shutdown. If it turns out you need an ignition computer for cheap I can get you a good used one. Hopefully it isn't broken, but theres really only two ways to find out: Find out its a relay or something that broke instead of the computer (check the ones under passenger dash) or get a friend's working computer and see if it fixes the problem. Be sure to use one from an '84 240 because they changed around quite a bit in the '83-'85 year span. Good luck with the fix.
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Isaac Babcock - '83 245DL and '83 244ti, "Sounds to me like I am right.." -JakeJ