Newport Beach home builder William Lyon Homes posted fourth-quarter net income of $21.9 million, or $2.10 a share, compared with net income of $8.6 million, or 83 cents a share, for the 1998 fourth quarter. Sales advanced 32% to $173.6 million. The results for the 1999 fourth quarter reflect the combined operations of William Lyon Homes and Presley Homes. Net income for the year rose to $47.5 million, or $4.55 a share, from $9.9 million, or 94 cents a share, for 1998. Sales increased 19% to $440 million.