Air Pipes to Catalytic Converter Question-Photo added

This question was moved here for me in case there is a truck engine mechanic ( or at least somebody who knows) who would know the answer. (No luck on Class C)

Boils down to the question-- which of the two pipes on the catalytic converter on a 1991 E350 460 EFI goes to the secondary air pump pipe that comes down from that on the passenger side at the back of the engine?

The top one in the middle of the Cat or the pipe at the front of the Cat?

Thanks