Thanks for this post; it's a bit more reassuring (and sorry that I am responding to an old message). I see tons of people with trouble, in spite of the simplistic-looking instructions, and it almost discouraged me from trying this--or, rather, intimated me. One question for you, though: I hadn't seen step #3 before... I just heard of replacing about two files in the El Cap disk; is step #3 something necessary? What does it do?
-Thanks (BTW, what are your specs and how does it run? I'm running Mountain Lion now, and, although I'd like to have a fully current Mac OSX for the first time in many years, I am afraid that a possible drop in performance could occur and annoy the heck outta me. I have an SSD in this thing now, so that definitely helps, but even then... I still can't see it being any lighter than Mountain Lion. My current GPU (HD Radeon 6450) is also not too good, as my main GPU (Radeon 5770) is currently 'out of commission.')
If there is a chance that a simplified installer is coming I would wait for that.
I discovered on an earlier version that manually replacing the 2 files wasn't necessary if you had a 64 bit machine to run the install on. Simply running the pikeryosefix app did exactly what was needed. I imagine that they will create something similar, though it is a little tougher now with SIP in place. To turn it off you need to set something in NVRAM on the 1,1. They understand this better then I, but I imagine they have some good ideas.
What worked for me last night was running the whole install on a 2012 MB via USB Sata adapter, then booting into 10.10 on the MB and switching all 3 files out (2 in OS and 1 on Recovery partition)
I moved the drive to 1,1 and it booted right up, recovery worked, etc. May have been made easier by already having SIP off in NVRAM. But switching the 3 files out is much easier when you aren't using the El Cap install as boot disk.
One thing that I think many folks have a hard time wrapping their heads around is that a MP can have nearly an infinite number of boot drives. So the wise choice is to never EVER do this on your one and only OS disk. Any old spare HD you have can be used as a 10.9 or 10.10 basic install to work from. If you have an OS disk with lots of crucial licensed software you will be MUCH happier and safer if you back it up first. 1TB+ hard drives can be had for a song now.
Make your life easier and calmer by making a full restore image via disk utility, that way no matter what you can start back at your previous working install.
It runs great on my 2,1 with Dual 5365s and 18 Gigs of RAM. Using a PCIE SSD I am getting 700Mb/s read and writes, the machine flies, no indication it is from 2006. I started a thread in Mac Pro section as I noticed there wasn't one.
With a little forethought and planning there is no reason for this to be difficult or stressful. But having a full backup is key. Craigslist and EBay have used HDs for peanuts. You can even use old PATA/IDE ones in the optical bays. Don't need to be fast, you just need fallback options.