I would connect the two drives .... Win as A and PCLOS as B ...... and then go into the BIOS and select to boot from B.
That should allow PCLOS to boot, and when it has you can redo the Grub entry to include Windows, thus giving you both bootable.
Should you ever wish to take out the PCLOS drive, all you need to do is to change the BIOS back to boot A and Windows should boot without problems.
On the other hand if you wish to take out the Win drive that won't affect PCLOS at all .... except there will be an entry to boot Win which won't work (naturally).
Just my opinion ..... there are other ways to achieve this too ....