You need to figure out which spindles you have to order the disc conversion.
There appears to be two sizes; light and heavy duty.
The GVWR on the door tag should give you a good idea, but it would be smart to actually measure the bolt spacing on the back of the spindle. I don't have the numbers handy, but you should be able to do a search.
I haven't done the conversion, but read a number of threads on them and drove kick_the-reverb's van that had it done. I had to almost stand up on the pedal, it was that hard! However, he felt that while the effort was higher, it was liveable. There really isn't much room where the master is located for a booster, so you have a few choices...
Do the swap and live with high pedal effort.
Research remote vacuum boosters and hydraulic boosters.
Get deep and research pedal travel, ratios, and hydraulic sizing and come up with a good system yourself.
Make sure your steering and suspension are dialed in too.
Here are some results from the first page of a Google search for "Dodge A100 brake conversion"http://board.moparts.org/ubbthreads/showflat.php?Number=6019731http://www.ebay.com/itm/Dodge-A100-64-65-66-67-68-69-70-2200-front-disc-brake-/370852082276https://scarebird.com/index.php?route=product/product&product_id=127http://www.orchidlakecandles.com/manual.pdfhttp://www.sweptline.org/forums/viewtopic.php?f=20&t=24461http://www.thetruthaboutcars.com/tag/a100-hell-project/
So the answer is that there isn't a quick, cheap, standardized perfect answer for you, just like most things dealing with old Mopars!