Hi gums,
I still wonder about an annular duct
TurbineD said it all with, for example
all the external plumbing changes that would have been required
I have found 2 photographs which illustrate the plumbing nightmare and how tight it was to get 2 of the tubes out of the compressor case. For some reason I am not allowed to add attachments to my posts.
You can see them if you google J58 images though.