I bet you can't guess this model...

I just got back from a train show with (surprisingly) a single purchase. Can you guess what it is?

-It has a bulge on the cab roof.
-It's green and black with the road number 181.
-It was made by a company who is famous for making model trains a scale above it.
-It has old (horn hook) couplers.

I'm assuming it's the model in your avatar. I can already tell it's not a steam engine, so that's one thing. Is it made by Hornby judging by the third hint? I'd like to know what it actually is.

It's a Lionel EMD GP-30 in Burlington Northern fashion.