array(2) {
  [8] => array(2) {
    [0] => string(2) "63"
    [1] => string(2) "64"
  }
  [9] => array(2) {
    [0] => string(2) "78"
    [1] => string(2) "79"
  }
}

$ar = array(
  8 => array('63', '64'),
  9 => array('78', '79'),
);

print_r(Descartes($ar));

function Descartes() {
  $t = func_get_args();
  if(func_num_args() == 1) return call_user_func_array( __FUNCTION__, $t[0] ); 
  $a = array_shift($t);
  if(! is_array($a)) $a = array($a);
  $a = array_chunk($a, 1);
  do {
    $r = array();
    $b = array_shift($t);
    if(! is_array($b)) $b = array($b);
    foreach($a as $p)
        foreach(array_chunk($b, 1) as $q)
            $r[] = array_merge($p, $q);
    $a = $r;
  }while($t);
  return $r;
}