Done a bit more research and it 'seems' the only difference between the TA21 & TA22 carbs is the engine they are designed to work with. I could be wrong (and I don't have any TA22s to compare against), but it seems the castings/carb bodies are the same, linkage is the same, and so on. Basically the same carb - only difference I can see is that the TA22/MC21 spec carb is tuned differently for each cylinder, instead of the same settings for both with the MC18.

Does that sound right? Anyone know for sure?

Still not sure why my MC21 had TA21 carbs fitted, but going to work with them anyway.

Question is - block the PWJs or not? Easier to tune if you are making modifications? Does the same apply to the air-solenoid/chambers as well?