Hi,
Let me know what your luck is like. If there are subtle nuances that aren't there, I might be able to help guide you in some way shape or form, but overall my intuition tells me those should get you part of the sound. Particularly Black hole – that's a really flexible preset.
It's also worth noting… an equally large part of the Kevin Shields sound is the fact that he uses lots of drone strings and odd chord shapes. Again, standing in front of a large amp, that creates some really nice feedback.
And, of course, don't forget to turn your amp up (short of damaging your hearing, of course). I don't know much about Demeters, but I imagine they can get pretty loud. JCM 800s have a very unique sound though, there's no denying that…
