D, much of III is based on the Vatican bank scandal of that period. There have been a few books written about it one of which is God's Banker.

As far as tactics go, Michael is referring to those that can accompany any such deal that involves stratospheric dollar amounts. It has all the elements of international intrigue where you have powerful international players involved and perhaps even governments. The new pope Lamberto (John Paul I in real life) may have been planning to investigate the bank and that's why he may have been murdered. Keinszig was the bank's president who may have been imbezzeling for himself , but more likely for others also. Once Michael deposited the money, it becomes the bank's.