Thanks, Fabpig. The 2nd letter is I because FINAL had 2 and BIRTH didnt have an L at the end of it so the I is the only thing in common between the two.
L is the last letter because
CRAWL before there was BOAST with an A in the same place and it had none in the right place.
CRUNK had none as well so the CR are out.
BROWS had none so the W isn't the right and that left the L