I am thinking much more primitive ... Remove the exhaust manifolds and drop it in and see if it "fits" so that I can physically see it with my own eyes.

The OM617 and the 6.9 are just about the same length which is amazing IMO. I just measured them again.

They are about the same width when it comes to where the motor mount arms are sticking out on the L & R sides which is also amazing since the 6.9 appears so much larger and bulkier.