Found a site here about modding a jcm900. Seems like it'll improve everything I hate about the amp.
I was less treble and more bass and seems like this should work.

Here is the document

How much do you think this mod will cost?

Gibson lpj
Epiphone Les Paul Standard
Epiphone Les Paul 1960's Tribute Plus
Schecter s-1
Marshall JCM900 100WATT HEAD
Fender mustang 1
Dunlop Crybaby
Danelectro Distortion
Tanglewood exotic electro acoustic
Westfield Bass