I have the separate sale 20-3297-1 K4. If you love the Loewy designed Art Deco PRR engines, this one is a must have.
Of all my engines, these streamlined Pennsy ones (K4,T1,S1) are probably my favorite.
I usually run it with 7 MTH FOM passenger cars.
My only negative comment about the engine is the sound quality compared with Lionel.
It's really a nice engine.