Just match the "8E" in the serial number and the "164" in the part number. Then just buy the one with the closest date you can find. That usually does the trick.
B6 is a less than common preamp though, not sure I've even encountered that one yet. Is it a standard 0 1 2 3 head map, or an odd one with missing heads? Just wondering if it's possibly a 3Tb that was downgraded.
Edit: Nevermind, I just looked on DonorDrives.com and they've got ones with B6 that are the normal 0, 1, 2, 3 head map. Just don't panic if you get a donor with a different preamp. If the date is close the donor will often still work. I've used CC heads on B4 preamp drives plenty of times.