The Neon SCCA racers were swapping their rear disc brakes for rear drum brakes because there was no difference in performance and the rear drums were lighter than the rear discs. But, having driven both, I do prefer 4 wheel disc to front disc/rear drum, simply because there is better pedal feel, lower maintenance and the rear disc don't require adjusting all the time to keep perfectly performing brakes.
The often adjustments is subjective, for proficient working rear drum brakes you just have to read the Owners manual about how to activate the self-adjusters and do the simple procedure every once in a while, if its even necessary. If you want sports car like responsive brake performance, then you would need to do it more often, which for rear discs you never have to do it.
Probably your best approach would be to get the OEM parts catalogue for both year mini-vans and compare the part numbers between the with the options, obviously where the part numbers differ is the equipment you have to swap over.
In most cases (cause I don't the specifics for an '04 and '05 mini-van) since you have a donor car, you have to swap over everything from the knuckle on the axle over. If its rear independents suspension, you often have to swap over the entire knuckle.
It is possible they have a whole different axle for rear drums and rear discs, the parts catalogue will tell you that. Many cars with rear independent suspension have an entirely different knuckle for each brake type.
Then you get into the hydraulics and ABS.
Hydraulics, the pressures rear drums require are different than rear discs, so at the very least you need to swap proportioning valves. Because of the different required pressures, which change the overall required pressure, they may have different Master Cylinders and perhaps even different brake boosters. Since rear drums require a lot less pressure per stopping power, keeping the original Master Cylinder and Power Booster (if they are different) might result in needing much higher pedal pressure per stopping power than typical cars.
You also have to hope the lines are the same between drum and disc, its possible they are NOT and you have to swap over lines as well, which more than 10 year old lines are likely to break trying to disassemble them.
Then you get into the ABS system, and perhaps a few other systems tied into the ABS, like traction control, Stability control, roll mitigation, etc.... Its likely they use the different sensors for rear and drums and discs, but they plug into the same socket and work the same with the system. But you never know, perhaps there is a whole other ABS system for the different brake configurations, the parts catalogue can tell you that. The sensors are likely electrically the same, but physically different since they have to mount and read the tone teeth differently.
And finally, even if the part numbers for the ABS and electronic modules are the same, the swap may require some sort of electronic reconfiguring of the ABS and associated systems to make it understand it has rear discs now and NOT rear drums that might require different profiles/algorithms/programs/parameters. This would require the dealer's electronics tools and them doing some interaction with FCA Hq to modify the database at FCA Hq with the vehicles build specifications, so the electronic tool can get past the idiot proofing to allow the tech to reconfigure the electronics to work with the modification. And judging from what I've seen from a lot of Dealership service departments, that is going to be a huge hassle, you'll have to shop dealerships to find one with a quality service department that actually listen to the customer, communicate between the service writers and technicians, think outside the box and go the extra mile for the customer.
I've seen many service departments (of all brands) that are simple money mills, get the vehicle in and out the door and get the check for the inflated charges. They don't care if they did the job right or NOT. I simply installing a official Mopar Accessory hands free phone Bluetooth kit myself, that required the dealer to enable the module, I go to the dealership and after waiting in the waiting room for an hour and a half, the tech came in to find me cause he had no idea what I wanted done to the vehicle, nor how to do it. I had to re-explain everything I clearly explained to the service writer, then go get the service writer to get the instruction that came with the Accessory that I gave the service writer, and then give them to the tech that explained exactly what he needed to do and the exact sales code he needed to input into the system to update the FCA database on the vehicle configuration. I look at the Service Writer and asked, what exactly is your job again?
