Hello, I'm a diesel mechanic by trade, and I don't have a Porsche. However, under the condition you have stated "possible" turbo seals are universal. So with that in mind, if I may suggest, looking at you oil pressure in the high rpm times when the smoking occurs. I don't know if you oil supply is restricted with a orifice or not. If no orifice and under high rpm, it could over pressure the turbo seals, causing a smoking condition. Just something to think about before you go out and buy a turbo. Also Contact turbo city in Orange, CA for pricing or their kits. If your turbo seal are going out and you mark you inlet impellers to out impellers (by scratching it) you can get away with replacing the seal/bushing or bearing yourself.
Hopes this helps