Canyon Carver project?

Well with that A833od and the 3.23/3.55s, you're gonna need a bigger engine. A lot bigger.Or you're gonna need to shed a lot of weight; a LOT. Or both. The ratios in that box are so far apart that you will have to run an unusual camshaft, and rely on some cubes to make it all happen. And you might as well forget the 25 mpgs.

Or you could start over and supercharge it. Then you can keep the 318, and that od box, and maybe even the 3.23/3.55s, altho with the od box I dunno why you would want to. A cruize gear of 2.36 is pretty darn low, making 65~1900 with 27" tires.
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I ran that box,
and those gears
with a 367 and a 223* cam.
And I can tell you that my 11/1 aluminum headed torque-monster engine was too small for performance driving in any gear except first. But I can also tell you that it far surpassed 25mpg. Soon I was running it with 4.30s,and a GVOD,and starting splitting gears. That worked pretty good, and I was able to swap out the 4.30s; first to 3.91s and then to 3.55s.
The ratios were 3.09-2.41-1.67-1.30-1.00-.78od-.54od Yeah that's right 7 gears, and all great splits. But I got tired of HAVING to split the gears most of the time, and in the end I ditched that box.
With a 318 it will only be worse.
Unless you supercharge it.