Replaing Tdi300 engine with TDi200 engine?

Hi, I have a Tdi300 whose engine has developed a high back pressure coming through the breather hose.

|I presume I will need to overhaul this engine. if so, I would rather look for a Tdi 200 engine which I find more quiet and reliable. Any place where I can get a used engine?

At the same time, I understand that a Nissan QD32 engine makes a good substitute and fits with minor modification.

Is it possible to get feedback on both options?

Regards.