Another interesting 6500 series flat is 6506. This one has a swivel plate mounted at the very center of the car. This would be for loads that need to straddle two flat cars. There is a classic shot by Richardson in 1946 that shows a very large tank on two fishbelly flats pulled by 454 headed for Farmington. 6506 was probably involved but you can't prove it from the picture. Thank you Dick for finding the Richardson shot that I had a memory of but couldn't remember which book it was from. The book was Narrow Gauge Country pg 102. I should also thank Randy for pointing out this unique feature so that I could bring back the photo.
Dave