I've been looking for a step bumper for the Aerostar without success. I looked at a number of vehicles' with stock step bumpers or aftermarket, and found that the '92-97' Suburban and Tahoe bumpers are about right, albeit about 1-1/2" to 2" wider per side than the stock plastic bumper. Nothing else seemed to fit the width properly. In any case, I used the Suburban bumper and will eventually fill out the sides with some diamond plate aluminum. For mounting brackets I would have used 5" x 1/4" steel angle, but couldn't find any, so went with 5" x 3/8" aluminum (also easier to drill). I put two pieces 6" total height back to back to form a T section 3/4" thick at the bumper mount. The upper mounting holes on the Aerostar chassis are at the same nominal height as the holes needed for the Suburban bumper. If you plan to use this for towing (my Suburban bumper has ball holes rated for 4000#--this is more than the Aerostar towing capacity), you should figure out how to support the bracket upper portions at both the front and rear walls of the Aerostar box section for additional support (try using studs with lock nuts at both walls). 12mm fasteners are used throughout. If people beg me, I'll show them some pix--assuming I remember to check back with this forum, which I last did probably two years ago...
You can see some pix if you search under "diamond plate bumper" or some such, as I posted them there...

 

yes some pix would be nice.

 

http://www.hitchdepotusa.com/index.cfm/event/hitch/

If I was gonna ever tow with my '95, I'd install a receiver. I do realize the thread is specifically about a step bumper retrofit and not primarily about towing.
The more I think about it, the Aerostar would benefit nicely from an aftermarket step bumper. Would be even nicer if it was designed with one in the first place.

 

I was looking at different truck & RV bumpers and one in particular caught my attention:

it is as tall as the Aerostar bumper cover,
it is a step bumper,
it is made of steel,
it is adjustable for width: there is one stationary Center section that contains the Step, and two side sections that can be extended or compressed, then tightened.in place.
it is a Ford truck, custom made for Veterinaries and Pet Groomers.
Made by Wagn' Tails in Indiana.