4.3 motor swap
Yep, no difference between a 2WD motor and a 4WD motor, ther might be some slight differance in the manifold in but if so you can just swap them.
The oil pans and oil pump pickup tube are different between two and four wheel drive. The four wheel drive also has a different oil filter adapter. You can swap these parts from the old motor to the new, but the oil pan needs to be aligned when installing it. The bottom half of the oil pan bolts to the transmission when installed. So if its not lined up correctly leaks or a broken oil pan will be the result.
Search General Questions