[phenixbb] is derivative data useful for looking for the missing part of the model?

Hi everyone, I got a partial model, consisting of 80% of the whole molecule, from the molecular replacement. The native data reflects to 2.3 A, and now the R/Rfree= 0.22/0.28. My problem is that the missing part of the model is important for us, but there is not any density for this region now. Meantime, we have several heavy atom derivative data. My question is that if refine the model against the derivative data, will the heavy atom appear in the difference map if existing? Any suggestions on how to use the derivative data to locate the missing part of model? Thanks in advance! Regards, Fengyun