Where to go for brakes on a 1999 Ford Class C E350?

Yes, E350 is "One-Ton" but that said, a One-Ton F350 is likely to be more robust in the chassis than an E350. I think the brakes are different, at least they were four our 2002 E450. It turned out that in that year, all "Super Duty Vans" like E250/350/450, single and dual wheel, used the same front disk brake parts. But F-Series was different.
If you're having the work done by a shop, they'll figure it out. Hopefully when they order parts. If not, when "Dem Holes Don't Line Up."