Was trading information with David and wanted to share his information on this topic. Thanks David as always.
"To answer your question of what they are- Autolite or Motorcraft- It doesn't matter. As I've said, you can't be sure of what FoMoCo did on a change over. FoMoCo used an "Empty bin" policy. That means they used up the old parts before breaking out the new parts. So what happens in a transition year is anybody's guess. What are that labeled? I can tell you that both have round topped float bowl lids and an external choke unloader assembly used on 2100s from 1970 - 74. Earlier 2100s have a flat top lid and internal choke unloaders. I'd take a closer look at the one on the right in the picture. Where the fuel enters is in a more usual place than the one on the left. The right side one will use a more common gasket. It also has a simplier linkage system, making it easier to adapt to your use.
Also look down the throat, under the choke butterfly valve. If either has a variable venture (aka VVI), you will see a moveable apparatus over the squirters and air bleeds. IF either carb doesn't that would also be my 1st choice. If the VVI system is right, right out of the box, it has some advantages in transitions, but it is harder to tune, in adapting it to not quite right situations. Both are early transition carbs and not too encumbered with EPA crutches yet.
My first Autolite 2100 on a six was the one on the left, on my 250, when I first put it together. I've been experimenting with 2100s and 2300s since and have one more 1.23 to assess. IF it doesn't work out perfectly, and quickly, I may just go back to the 1.08. It had an electric choke, ran clean and gave good mileage and power.
The advantage of the 1970 to 1974 2100s is that the internal choke unloader piston is eliminated and replaced with a new and different choke diaphram assembly place on top. This choke unloader system does not allow dirt or contaminants to be drawn into the choke, carb or engine.
Check the jet numbers on both and check to see if the power valve is color coded or not. Also check to see the number of holes in the accelerator pump rod and the over-reach rod. These will be useful information when it come time to fine tune. I'm assuming that you will put a rebuild kit into this carb before using it."
Bill
