The dosdude1 APFS patch for the boot rom works fine on the Mac Pro 3,1. Several people here have used it for this model (including me).
Maybe we could create a list of known good patched models?
The reason it failed on at least one other MacBook model was mis-identification of the EEPROM. dosdude 1 is working on fixing that.
The patch creates a backup .bin of the rom, patches it and writes the patched .bin back to the rom, which is where the fail occurs. So there is a backup of the original boot rom .bin file at the root of the disk.
If it goes wrong, all is not lost because there is a way of writing the original .bin back to the boot rom. You need a raspberry pi, a Pegasus clip for the SOIC8 chip and some patience.
The how to is here:
https://ghostlyhaks.com/blog/blog/hacking/18-apple-efi-bypass
The clip and cable can be got at Amazon.
[doublepost=1532171575][/doublepost]As to the theory that the boot rom is being overwritten/duplicated to cause the double ram post. I doubt it very much.
First, when a boot rom is rewritten, you'll see the much thicker boot progress bar and I don't think anyone has. Second, the HS/Mojave OSes do not have boot-rom patch code for Macs earlier than models that could run HS with APFS, so any model earlier than that (about late 2009/early 2010) cannot get an update without a lot of non-Apple effort. If your Mac is a model that never supported APFS with HS, there is no boot rom code that can be patched to it, so no double patch.
In summary, I think the double chime is due to something else, but I'm open to being proven wrong.
BTW, there is also a patch to the boot rom code for the Mac Pro 3,1, 4,1 and 5,1 that adds NVMe booting with the right card and NVMe SSD.