welcome to the forum its a great place to get your questions answered. If I remember right the E450 was use but had a slightly smaller V10 in hp and actual size (larger heads on the F53) then the F53 chassis.
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No clue but that small a unit on a E-450 is awesome! We have a 31' on the E-450 and it works very well. Everything I can find about your unit shows they typically came on E-350 chassis. They might have run short at the factory and just grabbed the next available chassis to fill an order, or it could have been an SO. Interesting that for the 2017 model year they appear to have switched to the Chevy 4500.