The Porter Cable machines are undoubtedly the best belt sanders ever made on Earth. That middle one, the 503, is a version of the streamlined "Locomotive" A3 leading the pack. When last sold by the now dumbed down Porter Cable it went for around 1,200 dollars. Its looks are more Syd Mead angular. $200.00 on eBay made this a steal.
Worm drive sanders – Porter Cable A3, Porter Cable-Rockwell 503, and Skil 448.
By the way, for locals, I'm selling a Rockwell 361, here