recovering faded manuscript using phtoshop

Sorry to  disappoint, but I am afraid that image may not yield enough data anymore and you may have to look into alternative camera techniques that cover a part of the spectrum that is less affected by the fading. 

I am no expert in that field, so my surmise is possibly no more meaningful than the »CSI-enhance-image«-bs, but based on the word-dropping in movies and such I wonder if infrared or even X-Ray might be useful depending on the ink used (organic, metallic, .?). 

In Photoshop itself one should, in such a case, start by viewing the three channels separately to discern if one offers more detail/contrast that the others. 
Then Sharpening and Adjustment Layers can be used to improve those contrasts. 

I just couldn’t find enough in this image so far. 

But are the original scans 16bit by any chance? In which file format have they been stored? 

Maybe there may be a little more to work with yet. 

And to make sure: The marked regions should be more or less full of type?