It looks very similar to the AHM/Rivarossi "Casey Jones" but I don't believe it is. The wheel spacing is incorrect for the old "999" as all three drivers would be the same distance apart. The pilot wheels would be spoked, it would have the more proper looking long, pointed "cowcatcher" pilot and a smaller tender. There is also a very distinct celestiary roof, very similar to old time passenger cars. Bowser and Varney put ones out similar to yours that were incorrectly called "Casey Jones" but are more correctly called ten wheelers. Because of all the plastic, it couldn't be either of those as they were primarily metal with Varney selling out to Bowser long ago.
Which leads me to believe that it is a Life-Like issue from the 70s. It has all the Pennsy markings, the squared up Belpaire firebox just ahead of the cab, the cylinder mounted on the pilot, the horizontal rather than vertical spokes on the shallow "cowcatcher" pilot being the ones that stand out. You should be able to run it without the tender as well. The final clincher is that I owned one of those Life-Like ones back in 1976, my first loco I ever bought with my own money. My first redetailing project too, I gormed it up like an early version of "Pimp My Locomotive"...sigh...
...I go back in my cave now...:thumb: