About this time of year in 1975 I attended P&W's 50th anniversary open house in E. Hartford. They had gone to a great deal of trouble to gather one each of virtually every engine they ever made, even borrowing Wasp serial number 1 (1925) from the Smithsonian. Each engine had a placard describing weight, performance, # built etc. I was particularly interested in the piston engines, but when I had my fill of that I deigned to visit the turbines.
At the end of the display was the biggest damn straight jet I had ever seen. It was missing the display placard, but I discovered the nameplate - a J58. Wow! It seemed to be about five feet inlet diameter - I'd never seen such a monster.
But then some years later at Dayton' Air Force Museum, a SR-71 (or perhaps A-12) had recently arrived. Next to it was a big engine, J58 nameplate, but it didn't seem to me as big as the one I saw out East. What I'm gleaning from this thread is that the AFM's J58 REALLY WAS smaller than the one at P&W.
In the 50's there were three similar engine mockups in shape. The JT-9, the JT-11 and the JT-12 (I couldn't tell them apart looking at the cut-a-way drawings)
The JT-12 we widely know today went on to power many business type or exec type aircraft and at least one with an afterburner
The JT-11 was developed for the government as the J58 powering the SR71
The JT-9 never made it to the supersonic bomber but was the largest of these similar shapes and maybe the one that you recall. The mockup of the JT-11 (Pre J58) still sits in the museum at P&W today and it's externals look nothing like the J58 today.