Help identifying JCM 800 mod

[ClassicRock88]

Hello. I have a 1988 JCM 800 2204 that has had several modifications performed, and I am trying to find out more information about the amp. I purchased it in 2010 from a gentleman in Springfield, Illinois. He told me that there was a tube effects loop and a gain modification to the high input. He also told me that the amp had been built by a guy in Texas (NOT Lee Jackson - still only 3 preamp tubes) that was known for modifying JCM 800's. The effects loop is beautifully installed and looks like it could be factory, except that the jacks use silver trim nuts versus the black ones on the rest of the jacks. The amp has been modified to run EL34's. The low input is stock, but as soon as you plug in to the high input it starts to hiss. On the high input you can get 70's hard rock sounds with the gain on 2. The highest I have ever run the preamp is 7 because it almost becomes unusable past that. When I took it to my tech (Obeid Khan of Reason Amps) I asked him if he could reverse the gain mod. After looking at the amp he said that it was not a simple one stage gain mod and he didn't think he could take it back to stock. He said he could probably map the signal path and try to cool it down a bit but if I like the amp as is that I should leave it. That's what I decided to do. It doesn't take pedals well but it has a beautiful, rich sound that still retains the JCM 800 cut. It just doesn't sound barky like you expect from them. The only other clues that I've got are visual. Jim Marshall's signature was filed off of the front panel and the amp was reupholstered in black levant rather than the elephant tolex on stock 800's. Does anybody have any ideas who built this amp?