I think you're missing the point.
The deep first gear is followed by a second gear about half the ratio. The rpm drop from 1 to 2 is tremendous. For stock engines with a wide torque curve, this is fine. For an engine with a narrower power band, (Like most 340s or 360s with a long duration cam) the shift to 2nd puts the rpms at the bottom of the torque curve instead of in the middle of it. Close ratio transmissions are ideal for performance engines. The 833 OD is fine from 2nd through 4th/OD if you have some decent axle gearing. The OPs slant six would do fine with a 3.23 or 3.55 gear and this T-5 transmission as well as an 833 OD.