I don't have a Lionel GP35, but I do have an MTH non-powered version. I would put the details for the MTH slightly behind the afore mentioned Atlas, but when next to each other, the MTH is a little "chunky", slightly wider than the Atlas model.
Here's some shot's that include the MTH GP35 (#6142)...
I picked the Atlas (#6135) up for a song ($156; new) so I had to pick it up, but paid full price for the MTH (albeit inexpensive compared to Lionel's dummy), and can't afford a Legacy set. I have a pair that I'm ecstatic over, so I'm not looking to add to it, and after swapping out the generic RS for EMD specific (see my post here: Specific Railsounds), this trio sound as good as they look.
BTW... The TMCC1 GP30 in the 3rd position is there because it doesn't have the see-through pilot foot boards like the other two, but sounds fantastic!
Thanks,
- Mario.