Rockauto parts search 1994 P30 7.4 is listing parts for a 5.7 throttle body not 7.4 throttle body.

Rockauto parts search 1994 C3500 7.4 liter. Often 2 each of the 5.7 throttle body spacer gaskets are included in 7.4 kits.

https://www.rockauto.com/en/moreinfo...12939&jsn=1037

https://www.rockauto.com/en/moreinfo...12939&jsn=1039

https://www.rockauto.com/en/moreinfo...=1038&jsn=1038