833 23 vs.18 on 440/6

I am running an a833 cast iron overdrive 4 speed transmission in my 68 barracuda fastback. My engine is a 440 sixpack and my rear is a 391 suregrip(489 case). I only have traction problems and large amount of fuel consumption. Lol. I say go for it... I have thoroughly tested this match.
I am running the 11 flywheel so I had to alter/fab my z bar. I am not 100% sure if the 10 1/2 and 11 bells are different on the big blocks... I don't remember.