Ford states in ads that all E-Series can tow up to 10,000 pounds.
As long as the Gross Combined Weight Rating isn't exceeded, it shouldn't make much difference whether it's an E-350 or E-450. The weak link may very well be in the hitch and frame extension (that's what would concern me most), and those appear the same after Thor upgraded from 5,000- to 8,000-pound receiver.
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