Your E-350 chassis is based on original Econoline van chassis, which is very different than the more truck-based F-53 chassis. The CHF applies only to F-53, which is normally on larger motorhomes.
An easy way to see the difference is that E-Series (350 or 450) use 16-inch wheels, while larger F-53 use 19.5- or 22.5-inch wheels and tires.
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