High Sierra install: "An error occurred while verifying firmware"

I have read many other threads on this topic, but none either worked, or seemed to fit my situation.

27" iMac 12,2 (Mid 2011)

Boot ROM Version: IM121.0047.B0A

SMC Version (system): 1.72f1

Non-factory HDD installed when the computer was new

So I think my problem is with the non-original HDD. I replaced the Western Digital 1TB drive with the identical product in a 2TB version. Except it's not identical, and Apple got even with me by not playing well with that drive. Had to install a separate app (HDD Fan Control) to track the drive's cooling needs. EFI Firmware Updates were always a hassle.

I have run diskutil repairdisk, with and without "repairdisk" in and out of recovery mode but it doesn't report any problems in the first place. High Sierra install always runs partway, then does the long "system beep", and seems to quit trying to install a few minutes after that.

I do not have the original HDD from seven years ago, and have not found anything that seems to address my particular situation. I've tried updating firmware, but the only references I've found for that are outdated and don't match what I seem to have already. Any suggestions would be welcome, and thanks very much!