Caliper Clearance + Tire Question

In the front you're not going to be able to run more than a 215 with the Ansen's anyway, those wheels in a 15x7 can only be had with at most a 4" backspace, which means the best you'll do and still clear the fender is a 215/60/15, and that will be pretty close.

Skidding the tire is not a good measurement for brake performance, it never has been and it never will be. You can lock up a wheel with a fast stab of the brakes with much less force than you can apply if you keep the wheel rolling. That's just the physics of friction. The Wilwoods will not be "too much brake" for a 215. They're not even that great as far as disk brakes go, the factory 73+ disks produce more clamping force than that wilwood kit can. And the factory didn't think it was a problem, even running bias ply's on the BBP disk cars.

In the back with a set of 275's you won't have too much brake with a disk either. This has been shown again and again, Mopar muscle did a rear disk conversion on a '73 Dart Sport and checked the stopping distances between the rear drums and rear disks from 60-0. Their result was that from 60 mph factory disks up front and factory drums in the back the car took 133 feet, 6 inches to stop. After the rear disk conversion, the stoping distance improved to 122 feet 4 inches.

The online article is a total mess now, probably something with being converted over or moved to Hot Rod when MM was bought out. The final distance used to be a caption on the second to last picture, but I don't see the captions popping up anymore. The hardcopy article is easier to follow, but that's the way it goes.

Rear Disc Brakes - All Bound Up - Mopar Muscle Magazine

Here's a Road Test Report on a '71 340 Demon, this is a drum/drum car. The stopping distances were absolutely abysmal, for anyone that says drum/drum is ok on the street today. The Road Test guys said they expected a 60-0 of 155 to 165 feet. What they actually got was a stopping distance of 169 ft, on a 3,250 lb car with E70's. That was their "best" distance, not an average of their results but a one off. Their Demon had 10" drums and a power booster. They did say their road surface wasn't ideal, but dang.

Vintage Road Test: 1971 Dodge Demon 340 – Road Test Magazine Takes A Real Devil For A Spin

Just changing from bias-ply's to radials adds a ton of traction, which means you can upgrade brakes even if you're keeping factory size tires. Start running wide tires and you can add a lot more braking than the factory provided originally for the SBP cars.