switching from 904 to a A500 or A518, anyone done this?

I'm currently running 225/50-17" Goodyear Vector tires.

The smogger 318 I have in the car doesn't have much low end torque, so the 3.55 helps with that.
I am in the progress of building a 10.5:1cr 360 at the moment, and I think 3.23 gears might work as well with a stronger engine.