The rotation of the right fuel tank elbow fitting within the tank during previous maintenance. The improper alignment resulted in the fuel pick-up tube being mis-positioned and a subsequent starvation of fuel to the engine. Contributing factors were the non-installation of an anti-rotation bracket to secure the elbow fitting, the kit manufacturer's failure to issue a notice of the bracket design to previous aircraft owners, and the pilot's not establishing/maintaining a proper rate of descent resulting in a hard landing.