Table schema:
CREATE TABLE table_name_55 (chassis VARCHAR, points VARCHAR, engine VARCHAR, entrant VARCHAR)

Question: What is the chassis of Officine Alfieri Maserati with a Maserati Straight-6 engine and fewer than 6 points?
SQL: SELECT chassis FROM table_name_55 WHERE engine = "maserati straight-6" AND entrant = "officine alfieri maserati" AND points < 6