According to Reb Brown at Comic-Con, the studios were planning two crossover movies. Captain America (Reb Brown) and Spider-Man (Nicholas Hammond) from The Amazing Spider-Man (1977). The second was Captain America (Brown) and Lou Ferrigno/Bill Bixby from The Incredible Hulk (1978). Unfortunately, neither of these ever materialized.
Reb Brown is a big Captain America fan.
Reb Brown was the second actor to play Captain America. The first was Dick Purcell, who played Captain America in the 1944 serial.
Reb Brown was the only choice to play Captain America. Being a perfect fit the comic book criteria. He was also a martial artist and happened to be under contract for Universal Studios, which made this movie.
Dr. Wendy Day was played by two different actresses. Heather Menzies-Urich in this movie, and Connie Sellecca in Captain America II: Death Too Soon (1979).