What make of enclosure are you buying?
Anyway, I have taken Raid-1 drives from a QNAP Nas and mounted them 
successfully in a USB Enclosure.
Going the other way, I'd not even mount the drive readonly until I have 
checked to see if utilities such as 'gparted' can read the partition table.
HDD's are pretty cheap these days. I'd probably not risk any issues but 
buy a new HDD of the same or larger capacity and once the drive was 
partitioned, formatted and mounted, I would simply do a cp -av {source} 
{Destination}
Then my original drive is now a backup.
Just a few things to consider.
I've been doing a lot of this sort of thing recently when I've been 
sorting out my Photo Archive (2.7Tb, 120K+ images)
Stephen D
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