On Mercruiser's the transom assembly includes the trim/tilt cylinders, also think that includes power steering.
So adding at least 150 lbs. to Glastron's claims, plus add some for fluids.
Guessing OMC & Volvo had different transom assembly's and T&T systems, plus manifolds ..
While doing searches for motor weights, found a near 100 lbs. difference between 350's (MPI, 2V, 4V, 305 ci.,)
Numbers I listed were off Mercury's site.
Why is a Ford 460 only 850 lbs. ?