I don't think A-Square, or Art Alphin himself, had a very high opinion of the 458 Win Mag based on what is written in an early A-Square catalogue I have. This may explain why few A-Square rifles were produced in .458 Win Mag.
This is Art's take on the .458 Win Mag. "This is a popular cartridge as far as sales go, but failures in the field tarnish its image. The advertised velocity of 2040 fps is still inflated. Ordinary ammunition tends to be erratic, and, coupled with short barrels average velocities are normally below 2000 fps. Though the .458 may transmit some shock, it penetrates poorly. The shooter must be aware that even with perfect placement, penetration to the brain on a bull elephant is not guaranteed. With an A-Square rifle (10" twist) and A-Square ammunition (465gr. bullet at 2220 fps) only, the cartridge is acceptable for heavy and dangerous game at close ranges."

So buckstix according to Art Alphin you do now have an acceptable DG rifle.

BTW the Hannibal rifle stock is called a Coil-Chek. Without a c, even I have got it wrong in some posts.