I completely agree with Tom. How bad is your original DDEC engine? What kind of problems are you having with it?
Here are a few suggestions
if you want to convert a non DDEC to a DDEC engine:
I would first check to see if the non-DDEC camshafts and pistons can be used in a DDEC application.The fuel systems are different, DDEC system operates with higher pressures than a non DDEC system. I would use the DDEC ECM, blower with it's fuel pump, use the restricted fuel return line fitting from the DDEC engine,use the electronic injectors with their harnesses, the turbo from the DDEC engine,the L/bank cam pulley with the pulse wheel,and all sensors of course.Another very important thing to check is if the MUI (mechanical unit injector) heads can be used, or the EUI head is different - injector harness routing thru side of head, injector cups, etc.I'm sure some more folks will jump in with more info for you.