8p is the best bet. Not all CEGs have bolt on crown wheels, I have a CEG box which doesn't. I guess that's why you say 1994 mk3 but I'm not sure of the exact date they'd change over.
So do mk4 boxes have different internals then? What makes them weaker, out of interest?
I'd say 8p because they are easy to find, pretty much any 5 speed mk3 polo or mk2 polo will have one. But yeah you can't fit an LSD to one.