One-time quasi-sync needed - best way to accomplish?
 

iMac has been smart updating an SD clone on an existing FW400 LaCie external on a once-a-week basis for over a year. iMac recently had logic board issue that prevented screen from displaying any data - this occurred very suddenly on a Thursday, with the latest SD backup the previous Sunday. Without visible screen or external monitor, no simple way to force an update to the clone before taking iMac in for service, so booted another Mac from external FW drive and have been using that for the roughly 2 week period while the iMac is being repaired.

Question is this - is there a way to update the external drive with the 4 days (Sunday-Thursday) of data from the internal iMac drive after it comes back from service and/or restore to the internal drive without overwriting those same 4 days worth of data? It's as if I have two sources that are non-contiguous masters and need to somehow sync one of them so it has all the data intact.

Seems like 'copy different' or 'copy newer' from external to internal might do the trick, but it'd be great to get confirmation before starting the process.

Thanks in advance for any help you can provide. SD rocks!

No easy way, no: copy newer/different isn't going to do what you want, really, because the result will be too mixed up. Perhaps use a spotlight search to find files that have been modified since that day and drag the important ones to the backup, then restore?