just do it!! i sprayed some of that flameproof paint DIRECTLY on the exhaust to see how it held up, and about 3-4 months later, it was still there, and that was without any prep
so i think u'll be fine with it on the turbo, just make sure u sand/wire brush the turbo before u do it
and degrease it with acetone/brake cleaner to get a good base, only problem is u have to bake the turbo to cure the paint