Just as a heads up; unless you have the correct tooling, installing cast iron drums is not a do it your self home project. If you have not done so yet, I suggest googling "fordbarn; cast iron drums"
for example;
https://www.fordbarn.com/forum/showthread.php?t=263496
Most shops that can turn drums will not have the arbors to mount the Model A hubs to center after the drum is installed. Also before the drums are mounted the flanges on the hubs need to be checked for run out.
If you have the hole saw like sold by suppliers, you can remove the old drums to save on shipping, but that might be a wash considering the cost of a good hole saw?