I think that will repair quite easily. Make or find a soft wooden dowl that just fits inside the chamber. Then use a hide mallet to gently tap it back into shape. Threading anything into it whilst its dented will tend to cut the metal, gently tapping with the dowl inside is just the opposite of what happened when you dropped it. I do feel your pain, that sinking feeling when you damage a rare or fragile part...

There is no 'logic' behind the Amal nomenclature. The 1C was fitted to some Panther models, so perhaps angled ?

The main variations are the length of the arm, the angle and the type of connection - Banjo or union nut with the possibility of top feeds as well.

Post-war chambers have a thicker bead along the top edge and at some point the size of the drain plug was altered...neither of these have any practical effec.

The main problem with second hand chambers is that in addition to the thread which can be examined, the condition of the float needle seat is a bit of a lottery and rectification is not guaranteeed to succeed.