I think your main problem with the brake is the actual caliper design...not original to the bike, no doubt. The cheap solution:Brakes - Front and Rear Brake Cruiser Set | BikeWorldUSA | Bicycle Parts and Bike Accessories
. I used this on my restored cruiser (with a springer fork) and they work/fit fine. They are made a little wider to fit around the wider tires. I also have fenders making it even wider to get the arms around...no problems. I too have painted rims and, yes, the pads will scuff and scratch. Nature of the beast. I only used the caliper in severe stopping situations as my main front braking came from a rear coaster hub brake setup.
A more expensive solution, I switched to this: 26" FRONT WHEEL WITH DRUM BRAKE HUB: Husky Bicycles
recently and like ZevO says, its a great brake and wheel. I painted the rim so I'm back in business.
I'm curious about the attitude of your springer though. The coil seems to be in a steep downward orientation and I wonder if that may limit the space between the fork and springer struts. It might just look that way due to the angle of the shot and the wheel being cocked to the side, IDK.
OH, and lose the washer/spacer. There is nothing to grip the caliper to keep it centered with that thing in there. The first time you brake, the caliper will pull over to one side and stay there. If you get it to work at all.