in too deep: trying to go BBP on a 68 barracuda and its going.. poorly.

OP
Nice ride!
As for a streeter;
As for the rear brakes, with four same-sized tires; here is my opinion.....
the factory rear brake proportioning is such that the rear brakes contribute very little to your stopping performance. For a streeter, this has been the norm for decades. I see no good reason to upsize the rear brakes unless you run big and little tires; and even then, you can re-engineer the 9incher performance with some combination of wheel-cylinder size and/or line pressure.
On the front, 235s are about all that fit without modifications, and so, the contact patch is gonna be limited. So then, on the street, when you upgrade your front brakes, they can very quickly overcome your tires.
On the back, it is possible to install 295s, and I did. This allowed me to re-engineer the rear brakes to do more work than the factory set up could. So much so, that my rear 10" shoes wear out about two or three times as often as the KH 4-piston units up front do. The front tires gotta steer the car, so to prevent loc-up in turns, they are the limiting factor. Which is why my rear brakes do more of the work, which necessitated ever bigger tires for more contact patch.
I'm a defensive driver too, but I still beat the tar out of my car.... on the street.
If I had to run same-sized tires all around, I wouldda left the 9inchers back there.
BTW, yes the Barracuda has such big tubs in the back, that you can use adapters no problem. All us big-tub A-body guys in hi-school, ran them back in the late60s/early70s. Of course that was with period offset wheels. Shoot I still have a pair that I last ran into the late 70s.
Happy HotRodding