I have been doing some research and just cannot find enough information for what I am looking for.
I'm looking at Sun Yat Sen coinage from 1936 to 1943. Here are my questions -
1) 1 fen coins dated 1938 and 1939. Mintage figures seem that they are somewhat common (12 million and 75 million respectively). Catalog value does not seem that they are rare. I have not yet to see any. Have you seen them? This is an example struck in 1937

2) Transitional period in between 1939 and 1940. It seems that there is a mix of aluminum, brass coins struck. For instance in 1940, 1 fen was struck in both aluminum and brass. 2 fen was struck in brass yet 5 fen was struck in aluminum. Why? Was it because they were struck in different provinces where some metals were more difficult to procure? I don't have an example of the 1940 1 fen in brass...
1 fen

2 fen

5 fen

3) The existence of Shi Kwan brass coins. They seem to be a very different type. According to somewhere I read, these were struck in Yunnan. Can anyone confirm this?

4) Numista reckon the portraits featured are Lin Sen. There may be more catalog that refer him. I somewhat doubt this is right as I suspect they are all of Sun Yat Sen. I'm certain he was featured in earlier coins as well as on Taiwanese coins.

Thanking in advance