Hi Brian,
It would be interesting to get hold of Brown, William H. “J58/SR-71 Propulsion Integration,” Studies in Intelligence 26:2 (Summer 1982), 15-23. Probably be able to shed some light.
The only way I see to get a copy of this is through the CIA. It is declassified and is listed as an article on their web site. If you are interested, I could go through the process to attempt to get a copy and see what it says.