Spacer for BLI PRR P5a

As documented by Spookshow and others, the Broadway Limited P5a model suffers from poor performance due to the outermost trucks not making continious contact with the rail.  This spacer forces the trucks to stay lower and engage the rail.  Inspired by the spaces originally designed by John LeMErise (aka Lemosteam) on The Railwire, but were entirely designed by scratch myself.

See more details at Spookshow here: https://www.spookshow.net/loco/blip5a.html