Trying to get Power out of a 225

Do everything you can to build bottom end torque, and get ready to feed it a very serious torque converter.
If I had to identify any specific Slant weakness, its a lack of bottom end torque, which is a product of its unorthodox geometery. Too long a rod, too small a bore.
From 3000 up, they can really turn on. Out of the hole they are absolutely miserable.
The ironic thing, is that nearly all of the popular mods, bigger valves, cam, etc, only make it worse down low.