The oil pump seems to just be different in the oil filter required. The Sonata uses a timy one.
The important thing on trying to use the Sonata pump is that the oil pickup tube will have to bolt up to the oil pump exactly the same.
I imagine the sonata oil pan is pretty shallow, but mute point because you'll need that deep Montero pan, its baffles , and the dent that makes room for your front diff.
Did you find any hole on the bearing craidle for the tube to bolt to? There may be some, but they my be in a different place than needed . Be prepared to drill and tap those 6mm (as I recall) holes.
On your m.m. bosses, hopefully it was only the very last of these engines, like the 96-97 , that didn't come with the rear wheel drive mount bosses already tapped.