Lot of variables in this so..
Has it been setup recently, and what management u running?
Is it running well generally, could be remanufacturing fallout burning off..
What colours the smoke, and is it doing it when warm,cold or all time?
When u rebuilt engine, had/has the exhaust been left full of crap, or been stored in damp place esp if stainless?
If all the above are good then from what u describe it does sound turbo related but if the fuelling's shit it can make it puffy so as long as the turbos been rebuilt properly then id be getting it checked over for fuelling, or if in doubt pull induction pipes off turbo and check for play/oil getting into exhaust...
Sorry cant be much more help, but if all the basics are good then its sounding
abit more indepth...
GOOD LUCK
