You can fix it without finding 8.1
I was on the same hunt as you, but figured something else out.... My phone would take up to 5 mins to restart when I first installed ARHD 10.2 , but after flashing stock rom and recovery, I did a OTA update which took me to software version 2.23.666.2 , reflashed ARHD , and it now works like a charm!
HTC One M8
HTC One M7
Samsung Galaxy SIII
Samsung Galaxy SII