.00 нашел как убрать,
В system\library\cart\weight.php
return number_format($value, 2, $decimal_point, $thousand_point) . $this->weights[$weight_class_id]['unit'];
return number_format($value, 2, $decimal_point, $thousand_point);
заменил на
return preg_replace("/\.00/", "", number_format($value, 2, $decimal_point, $thousand_point) . $this->weights[$weight_class_id]['unit'] );
return preg_replace("/\.00/", "", number_format($value, 2, $decimal_point, $thousand_point) );
А вот г на гр. заменить и вывести вес в категориях не нашел пока.