I've only ever removed those clocks by removing the cluster first. I don't think it's possible to get to the three screws that hold it in the cluster, let alone trying to screw them back in.
As for the fix, I'd do the quartz clock conversion. You can buy the kits from Instrument Specialties, they sell on ebay too. I just did a conversion last month on a '70 rallye clock. It wasn't that hard, just take your time.