Welcome and Happy New Year to you too, N6560J!
I'm no Cummins expert, but when I was researching my purchase in '04, the Cummins exhaust brake function was performed by moving the vanes of the turbo. This may have been a newer version of the ISB to meet '04 emission standards, but if you can't see a separate brake, this may be the case for yours especially if you can see some sort of actuator attached to the turbo...
Good luck in '08!
'04 Journey 36G - Cat C7
'04 Honda CR-V