Adding to what spencerPJ said, you still need to verify things like brake & suspension parts, fan belts, alternators, etc. because E350 vans come in several configurations, with single vs dual wheel rear axles being a prominent one but not the only example.
However, I'm wondering if your Flair is really on the E350 van cutaway chassis. All the Flairs I'm familiar with used the F53 stripped motorhome chassis rather than a van and its parts are different than a van. The F53 is much closer to the F550 medium truck chassis. If the VIN has F53 in positions 5-7, it's an F53 rather than a van chassis.
+++Further research indicates that back in the day Ford did supply what they called an E350 stripped chassis, which appears to be essentially a van without the cab. If the VIN has E33, E29, E30 or E39 in digits 5-7, you probably have that chassis rather than the F53.