A Good Rebuild Is Better Than Scrapyard Assembly... Learned It Hardway...
Pros Of Assembly Swap
Time Saving..
Maybe Cheap.
Cons Of Assembly Swap
Decrease Car Value/Engine No Change...
Risk Of How Much Km's Done And How Much Life.... You May Even Waste All Efforts And It May Start Smoking After 1 Week Or 1 Month Worse Than Your Previous One... Usually They Are Almost Half + Done Life Motors Unless You Are Lucky Or Fine One In Mint Condition
So If You Find A Good Repair Shop.. You Can Just Change Required Parts With Cleaning ....Most Of Smoke Issues Arises Because Of Failed Valve Seals Or STuck Oil ring..
84k Is Nothing For Car ..It Might Be Abused Badly Causing This Or It Maybe Tempered Mileage....Usually 84k Is Where 1st Time It Opens For Timing Belt And Other Fluids Change...Not Rebuild...!