Something like this?
SELECT position FROM
(
SELECT
id, @rownum:=@rownum+1 position, archived
FROM blogs, (SELECT @rownum:=0) r WHERE archived ='N'
ORDER BY id DESC
)
AS position
WHERE id IN (SELECT id FROM(SELECT id,'', 'blogs' as mytable,title, content,
MATCH(title) AGAINST('keywords*' IN BOOLEAN MODE) * 8 +
MATCH(content) AGAINST('keywords*' IN BOOLEAN MODE) * 4
as score FROM blogs WHERE archived = 'N' AND MATCH(title, content)
AGAINST('keywords*' IN BOOLEAN MODE)
ORDER BY score DESC, id DESC)x)