[Milsurplus] BC-221 question for the pureists

[J. Forster]

Since I don't own one and am not familiar with them, what is the difference
between an SCR-221-x and a BC-221-x, where x can be any applicable letter(s)
like M or AH ?  I understand there are a bunch of options designated by the
letters.

Also, is there any good table or chart on-line that lists the options and suffix
numbers? A URL would be appreciated.

Finally, is there more than one type of AC power supply and were they all 'add
ins' or were some models originally delivered as AC line powered?

TIA,
-John