Ok - I have had troubles when I tried this in the past - I did not get Working HS before. But I thought maybe it was time to try again. Background - I have a late 2009 MacPro, flashed to 5.1 quite a while back. Its got the modded processor card: 3.33 gHz Hex core Intel Xeon, 24 Gig 1333mHz Ram, Nvidia GeForce GT120 512Meg, and an updated Wifi card.
Running Sierra 10.12.6 - I've currently got all conventional drives in the box. I own a 6GB OWC SSD, but pulled it last time this failed.
So last night I bought a fresh 16GB Kingston USB 3 stick on the way home, and formatted it properly. I downloaded a fresh copy of the DosDude Install patch tool (yes, I "know" it says its not needed, but since it has always failed, even back when the HS Betas were out, I thought it might help). Downloaded a fresh HS Install app - 5.21 GB., loaded the DosDude Tool and the HS Install app. rebooted to the thumb drive, did the install, and again, wound up with the Bad disk image when it completed.So, reboot, get to the recovery partition, run time-machine and restored to an hour previous to the attempt. The boot drive recovery partition said it was 10.13.5 (!). Time machine worked fine, I'm back on Sierra 10.12.6
I have no idea what to try next - can someone help?