In regard to US Agent and concerns,

From the sheet
"In the coming weeks John was trained in how to fight using a shield akin to Captain America and how to properly interact with the public. Now Johnathan Walker works as the U.S.Agent, spokesperson for the You-Men and professional crime fighter."

The Frank Simpson Captain America/Nuke doesn't use a shield or fight crime or engage in martial arts if he can avoid it.  He's a soldier, whacked out of his gourd more often than not on uppers and downers.  He's in Vietnam not the US and while I plan on him having an official unofficial Captain America designation I would also be fine with not doing that if it leads to confusion or toe stepping.

No offense taken MaoMao.  I'm planning on doing both.  The idea is Rogers' Captain America will be feeling his way out after a brief introduction and Simpsons' Captain America will be, as they say, in the shit.