There are those much more knowledgeable then I, but I would not guess your "thump" means tranny failure.
I've been lurking a long time and have never read anything like that.
More likely it's a tranny mount. That seems logical.
Does it do it also when you downshift? How many miles on the rebuilt? How is the fluid? If they made any screw ups it probabbly would have manifested itself catastrophically by now. That seems to be the way it goes with rebuilds.
4K for a southern 92 in very good shape is a fair to good deal. You seem to be one that would take care of it also. The SVX is unique in many ways. I say buy it, I know you'll enjoy it.
