Oh viking, you're playing with my emotions now!! A two door wagon!! See my gallery if you haven't yet, and you'll understand why.

As for the Merc stuff: I won't get into the trim as that's a bit hard to describe here. The major differences are the bumpers are a bit different, the grill has wider teeth and more of a peak across the middle rather than the gentle roll of the 49-50. That peak carries through to the park lenses which are more square looking, are larger, and more integrated looking as the trim outside the lenses extends around the front radius of the fenders.
The dash design is different, as is the steering wheel.
In back the rear window is very different. The 49-50 have a long ovoid shape, where as the 51 is larger and has squareish corners at the bottom. Even more distinctive is the way the quarter panels terminate. The 49-50 kind of roll down toward the bumper as they wrap around to line up with the deck lid, the tail lights are horizontal and wrap around with somewhat of a "tacked on" look. The 51 is more squared off with a higher line at the top, which fits well with the change to a vertical shaped tail lamp lense which has a more integrated look and they extend a few inches beyond the line of the deck lid.

My first car was a 51 Merc tudor, of course then, it was just an 11 year old used car! It was very special to me though.