There were a few delays to the project, but I got it finished today.
In theory, you should be able to find it following Mr_A's tunnel from the spawn, but I haven't gone that way myself. I do have a path which goes down from the spawn portal down to the lava level, and then follows from there to the two nether fortresses. I've signposted this route to the Blaze Farm.
(https://imagizer.imageshack.com/img923/7739/Mp91gK.png)
Great work! I really should finish that tunnel it kinda goes nowhere at the moment. I keep dying when I go to connect it up.
I just ran a 30 minute trial, where I culled the Blazes every 5 minutes.
It resulted in 249 rods (using looting III), which is about 8 per minute. I did note though that on two occasions, deaths due to cramming started occurring at about the 4:30 mark, and once a few seconds before the 4:00 mark, so the results should be a bit better if the blazes are culled every 4 minutes instead of 5.
Cool, thanks for building it.
I now have an operational slime farm as well, which can be found just in front of my base. It's not running terribly efficiently right now, as there are a lot of caverns near by and I haven't finished lighting them up yet, but it's better than it was when I first built it.
The best place to AFK right now is in my base. I am contemplating building an AFK room at y = 139, which will stop anything from spawning below the farm, but will only do so as a last resort due to aesthetics.