1. Do you want less bass, or more treble? The difference is what happens to the mids. If you know how to use Duncan's Tone Stack Calculator, see if you can get what you want by messing with the tone stack. If you have a breadboard, breadboard it and mess with C5, C6, C8 and C9.
2. There is plenty of info elsewhere in these forums on how to test JFETs, so I won't repeat it here. The good news is this circuit is pretty forgiving on JFET specs. Any Vp should work. Just make sure your J201s are in spec. Lotta garbage for sale.