Caps, I checked my local wrecker for that boot, and we turned up all but. (I think it is a 1W1 part after some research)
He is currently wrecking a '78 IT175 but no airbox fitted. the closest I could find is a 5x3(airbox) & 5x9(elbow attached to airbox), 175j I think?
I can send you that 125J elbow if you want to give it a go.