I don't have any experience with this, but please know we're all worrying with you. Has the vet done a stool test yet? I would think that would be one of the first things he'd do. Like you said, globulin levels being high could mean a lot of things, and we're going to pray that it's something treatable.
My boys' stomachs gurgle when they're hungry, so that part seem to be normal. The head tremors I wouldn't worry so much as well, every couple of months are normal.
If the vet calls back tomorrow and says he still doesn't know what's going on, I'd look for another. From experience, some vets are just more knowledgeable and can pin point what to look for and what needs to be done.