It appears that you have done a thorough job of ruling out everything other than the carburetor (which is the correct way to do troubleshooting in my opinion).
So what is next? The carburetor.
You mention that the model B wouldn't run the engine. Then you installed a carburetor which seemingly needs numerous manipulations to make it work on your engine. Not exactly plug and play it seems. Maybe it will work if you tweak it enough. Maybe the new carburetor is bad. It would have been cool if you could have bolted it on and be on your way, but it didn't. Now you are banging your head on the work bench (understandably so).
Time to regroup. Find someone who has a Model B from a running 235, or better yet, a carter 2100 who will loan it to you for trouble shooting purposes.
Carl
