I am not familiar with swapping these two engines but they are similar so I wouldn't doubt they are correct. However, I agree with your mechanic that this type of stuff just opens a can of worms. If it were me, I would try to return the engine and start over with a direct replacement even if you have to pay a little more. The only reason is, you could end up spending just as much or more trying to make this engine work. You could have someone do as they said and it works just fine but this is a risk and how do you put a value on this risk?
In my opinion it is not work the gamble. However, if you cannot return the engine then you have two options in my opinion. First, tell the mechanic that said he did not want to take it on that all you want him to do is swap the parts as instructed and install it. I assume he is concerned that this issue will become his if he does what they suggest and it still has issues.
The other option is to call around and find another mechanic that is willing to take this on.
Let me know what you find.
Monday, July 22nd, 2019 AT 7:18 PM