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I hear that later E-series vans (not sure of the years, maybe around '99?) had a Dana 60 rear axle with disk brakes and the older 8 on 6.5 bolt pattern. Probably all full floaters, but I'm not sure of that. That might be a path for you.
The biggest problem with rear disc kits are the parking brake. Some don't even have provisions for one, and others have a complex system to keep it, all of which is not the greatest.