Bill wrote:

the Optiarc 7240s internal drives seem to be about the same speed
as the external LG drive that has failed, and would be ideal for him if
they were external usb drives

Buy a USB-SATA adapter, they often come with a power brick and
molex-SATA power adapter ...

e.g. (but not a specific recommendation)
https:/amazon.co.uk/dp/B001A5SK56