The Dodge Red Ram "hemi" engine was introduced in 1953 with a displacement of 241 cubic inches, about 120 HP.
'55 saw it grow to 270 cu. in.
For '56 the deck was raised and displacement went up to 315.
In '57, it grew again to 325.
Far as I recall, it was available across the entire Dodge car lineup. The last high-performance D-500 twin-carb version made about 310 HP.
It's important to remember that it's different from the "poly" engine available somewhat concurrently, though the "poly" and Red Ram share the same tall deck block.
The Red Ram hemi has the smallest exterior dimensions of the Mopar hemi engine lineup, which is why it was used in Barris' Ala Kart.
The first issue AMT Ala Kart kit, and the later '29 Ford kits that include it, represent it roughly scale-correct.
The retooled Ala Kart engine is ridiculously UNDER scale, stupidly about 1/32, in a 1/25 scale model.