The problem with 1992-2007 E-Series (besides the OEM bars way too small for RV use!) is the way the Front Sway Bar pokes into bushings in the axles. If you can find an aftermarket kit with "hard" bushings, you might gain something on the front. It's just a poor design and it took Ford till 2008 to either realize it or acknowledge it and change the design back to End Links.
Those bushings in the axle are harder to change than end links, so develop a strategy. The auto parts chain stores like Autozone have loaner tools. It'd possible their "balljoint press" might have adapters that'd let you remove and install those odd bushings.
The OEM rear bar is designed well but it's way too small. If all you can swing right now is bushings, go ahead, but I think I'd replace rear first if I was only buying one.
You should see a difference with hard bushings, but it won't be the Day and Night difference you get with Hellwig bars.