Not really sure if you're gonna be able to do it. I've never looked up under a '67-'69 Cuda to see the area you'd be working with. I'm sure it'll fit with the correct measuring. Chris (B1Cuda) might have 12's on his Cuda. I can't remember, so I can't speak for him.

However, on my '72 Dart I had Alumastar wheels with double beadlocks, which increased my total wheel size to a little over 11" from the original 10". I ran the car with M/T 30x13.5 ET Street DOT's. They tucked decent for a minitub and stock framerail. If I ran a smaller tire I could've had the rear even lower. Had to trim the upper inner lip to let the car sit down on the tire a little without rubbing. Here's a pic.

Wes