[nq:2]"a whole dif'ernt thang"[/nq]
[nq:1]Or, "a whole 'nother thang"[/nq]
As a German enquirer, Peter probably needs at least one straightforward answer. No, it's not correct. Use "a wholly different thing", though in BrE it would more usually be "an entirely different thing". The use of "whole" in this kind of expression is informal, perhaps regional, AmE.
Alan Jones