@ Doug -- I have a Model 505 that I recently acquired. And unfortunately, I don't have a spare! LOL! If I did, I'd certainly fix it up and sell it to you! Also, I think Kirby introduced the 4 row brush roll sometime in the 80s. That was during the Heritage series and Kirby started making the small head (500 series) nozzle available on the Heritage. But again, I don't know exactly when that was. I have one of those small 500 style nozzles for a Heritage AND I also have a Heritage II Legend that I'll put it on some day when I get around to restoring it. But I'm pretty sure Kirby started making the 13 inch 4 row brush roll for the Heritage models.
@ Brian -- I don't know how rare the 3 amp 513s are. The one I have was in really awful shape when I got it. It had been sitting in someone's barn AND it was seriously bojacked with all kinds of awful blue trim. When I tore it down in order to rebuild it, I discovered that the motor in it was actually a 4 amp motor, even though the spec plate clearly says "3 amp". Fortunately, I had a spare 3 amp motor in good shape, so I installed it. Regarding the Model 511 -- I think you read my post on that. According to Charles Lester's website (1377731.com), the 511 is rare. In fact, he says that Kirby literature indicates that it wasn't built. Perhaps because of the Korean War? I don't know. All I know is that I own two! LOL! But I have a friend who also rebuilds Kirby vacuums tell me the same thing that the 511 is pretty rare. But the funny thing is that recently on Ebay, I've seen three different 511s, including the one I came upon in all original condition. So again, I can't say for sure. I think Charles Lester can shed far more light on that question.