Are your heroes traveling under their own devising, or are they somehow drawn to events like this Quantum Leap--style? I ask because it occurs to me that if I were to travel freely to 1975, I would buy as much stock in 20th Century Fox and Kenner Toys as I could get my hands on, sell everything after 1983, stick the money in the most secure, highest interest-bearing account I could find, then return to the present and cash in.
Just sayin'.