Why 1920s technology could not produce an Iowa

Would completed K3s cause Iowa-like battleships to appear years earlier?

No. The machinery and supporting technology that made Iowa possible did not exist in the 1920s.

An earlier naval race could accelerate design work, but it could not simply pull the Iowa class intact into the 1920s. The required engines, power density, and associated technologies had not yet matured. A contemporary American response would have to trade speed, armor, armament, or displacement within the engineering limits of its own generation. It would therefore be a substantially different ship even if it pursued a similar strategic role.