Whirlwind references back to Earthshaker by the "Visit the fault" road sign.
Likewise Funhouse back to Whirlwind with "Feel the power" road sign and the graphics at the Wind tunnel.
This indicates a pattern. However, I don't any other such references in PL games. Other than that Road Show apparently has a quote back to Rudy. One talking head to another.
To you know any other references between PL games.