Madkow, Im not a wizard with that 930 CIS, but have you tried pressure testing the turbo system? If there is indeed a boost leak, the mass. air door will be pulled down under spool-up and will disperse the fuel according to its position but the engine will not be getting the proper volume of air due to the boost leak. The only reason that this seems like a possibility to me is because you said the problem was under load, not during free revving.
86' 930/GT-40R Sold
94' Rustang GT daily