Upgrade from 7 1/4 to 8 3/4....how wide?

I have a 67 Cuda convert and I want to upgrade the rear end.

Someone locally is selling a 8 3/4 narrowed to 47 1/2 flange to flange. I don't plan on tubbing, so is that too narrow?

If it is too narrow, and I have one made, what length should I get? I'd like to slap some nice wide tires in the back to fill up the well.

Thanks.