Conversation so far:
Who were the Kangaroos?
Heffernan debuted as "The Fabulous Kangaroos" on 3 May 1957.
What did Al Costello have to do with them?
Costello and Heffernan debuted as.
How did they perform?
Only weeks after that first match, The Kangaroos were working with the top tag teams in the promotion.
How did things unfold after the promotion?
After working in Stampede for a while, The Fabulous Kangaroos started to travel across the United States.

Question: What else did they do during this time?
Self-contained rewrite: Aside from working in Stampede and traveling the US, what else did The Fabulous Kangaroos do during the late 1950s?