Husky does not list having floor liners for the E450, but they do for the E350. I had assumed they are identical but am I wrong? I don't want the hassle of returning them if they don't fit.
The cab is the same across all the Econoline series, floor mats for a E-150 would work if you are looking at seat forward.
The two cutaways (E-350 and E-450) have the same cab length from the factory, but different upfitters may change that dimension, by adding a rear extension between cab and box.