Is there any other rear that will work in my '65 barracuda??????

Seen a B-body rear in an early A myself. They're a little wide but fit.

For "forbidden" parts that come close to bolting in, the 8" or even 9" rear axles found in early Ford Mustangs, the Mavericks and Comets, and the Granada / Monarch / Versailles are the correct width. Never personally tried swapping them in, but I have brought a tape measure to the local boneyard to confirm this.

For shear lunacy, the dimensions suggest a '87-'92 Toyota Supra Turbo rear suspension is about the right width to fit under an A-body. It is about the same width as the B-body rear axle. Not something you'd be able to squeeze in there without a Sawzall and welding torch, but I've seen loonier suspension swaps made to work, and at least you don't have to deal with the challenge of narrowing an IRS. It's not likely to break, but it gets a lot worse traction than Mopar leaf springs behind a high powered motor.