disk on rear

i have a 8 3/4 rear end on my van and was wondering if i can convert it to disk?

Yes, do a search online. The main thing is that most kits require 'green bearings' so it's more involved than just a swap. Most or all require the bracket be welded to the housing also. Then you have to fabricate the lines and hoses.
I did it on my 40 Plymouth, using Ben Snobar's kit. I chose his due to no Green bearings, but was not thrilled with the kit.
You also have to chose how to handle the emergency brake. Some calipers have provisions for this, but are expensive. Then you have the cables to consider.
You might check into Jeep Cherokee rear axles, some have discs already. You will have to check widths and may have to redo the spring pads.

Don't forget the master cylinder either. You want one that will supply enough fluid to the calipers, the stock one will not.

thanks for the info!

Ive got to ask-What are "Green bearings"" never herd of this,

http://chucker54.stores.yahoo.net/rearaxbearki.html

They take out the tapered Mopar bearings that require an adjuster on one end to set lash/preload and replace them with ball bearings that do not need the adjuster.
There is controversy about them, with some feeling that the OE tapered bearing is a better design and worth the effort to set up VS the people that say the green bearings are fine and it removes an unneeded complexity.
They are similar to what GM used on the end of their axles.

Unless you are versed in axles and bearings, it's best to take your axles to a machine shop to replace the bearings. They are NOT easy without the proper tools and knowledge!!!

TRUE!! Ive done all sorts of ford & GM rears & axles - just never herd the term green brgs?? and as i have never done any chrysler stuff -makes sence tome - the tapered bearings are same as used in the early chev truck front axles and expensive to replace now so the regular bearings have kits to re-do them- interesting Thanx

here is a conversion link. http://www.magnumforceracing.com/store/detail.asp?ProductID=3092

here is a kit from jegs, http://www.jegs.com/p/Right-Stuff/Right-Stuff-Mopar-8-Dana-60-Rear-Disc-Brake-Conversion/1244429/10002/-1

I would like to add one more thing, since both links do not mention it.
There are different size center registers on the ends of the axles. I was warned of this by the supplier of my kit. I had to have the center (inside the lug studs) turned down to fit the caliper. Maybe these more modern kits use a rotor with a larger hole, relying on the studs to keep it located. Just one of the many things you must consider when instaling a kit on an axle assembly that was used on many cars and trucks over many years; some stuff will need work to fit!