If there are differences between them the important one to look for is the size of the inlet ID. Most all of what you have there should be around 5/8" for 196's. I'm guessing 212's may be slightly larger. And I know the 224 mufflers are 7/8" ID and the one to use if you want it stock muffler quiet with a more aggressive sound and better performance than a 196 muffler.
I was running a 3/4" header and silencer on my 196. The 224 muffler took it's place and the only difference I can tell is sound.
Someone was selling 224 mufflers on ebay and sold out 8 of them.
Yes, i agree. The 224 muffler is the perferred muffler. With a bump up in compression ratio, a cam and carb to match, you will hear and feel a difference with the 224 muffler. The ducar 212 muffler, is slightly bigger i.d. then the pred 212's, and 196 clones. But not as big as the 224.
They do interchange, might have to open the stud holes up a lil.