I am in the middle of replacing my engine too, so I've done a little research on this. From what I understand our 3.5L is just a stroked version of the original 3.2L so all of the exterior dimensions are the same for both engines and it should bolt right into place in the VX.
The theory as to why our 3.5's burn so much oil is that when Isuzu built the engines they just used some bad rings and pistons. The pistons in the 3.5 are very short so the rings are all crammed together. Also, the pistons only have a few oil drain holes in them that doesn't allow the oil to get back into the case so it gets burned in the cylinder. The new Isuzu pistons have ten or more drain holes in them and they have better rings, so the new (and sometimes rebuilt) engines don't have the oil burning issue. All of the pistons and rings in the 3.2's don't have those issues so no oil burning.
If your 3.5 is good, and you have the time, you can take the pistons out and drill the additional holes in the pistons to help stop any oil burning issues.
Good luck with your swap.
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