My e250 doesn't have a swaybar up front and for stability I think it could use it.
I have a bar on a E150 , Think it would work? If it fits.
I know it would be as strong as a E250 but since I have it, I hate to waste it.

 

For better replies to your questions always state your year too.

The fact a van has or has not been converted doesn't make a difference but the GCVW does. For the best results match the chassis to the sway bars, if possible always run a front and rear bar.

Front sway bars are fairly important because there's a lot of weight over the front suspension, while braking you'd want the better control those give you. Rear bars make a tremendous difference in how the van handles during evasive maneuvers. This of course assumes the bushings for each bar are in top condition. I use Hellwig front and rear bars but when stock OEM parts were in place I'd renew the bushings with urethane from vendors like Prothane or Energy Suspension.

A careful inspection and possible renewal of shocks, springs and maybe rear leaf bushings is a good idea too.

HTH