Sorry about that, working with too many images .. it should be grub.cfg in the grub directory .. on the dual boot image (EFI/Legacy) by setsunakawa. I am working on a Legacy image too and that one has the isolinux.cfg file. Thanks for catching my error, I went back and corrected my post.
Thanks for sharing! I'm now running -8451 update 1 with no issues so far