James P. McMahon Sr., a longtime financial exec for several studios, died March 5 of natural causes in Phoenix, Ariz. He was 74.McMahon, a native of Fort Dodge, Iowa, graduated from Northwestern U. and served in the Navy during WWII. A CPA, he worked for 20th Century Fox, Cinerama, MGM, Paramount and American Cinema. He retired as a senior financial VP for MGM-Lorimar Films Labs. He is survived by four children, a brother and sister and numerous grandchildren.