[Zeke]

Depending on the existing ducts you could consider using mini splits. It's not unusual to use up to five inside air handler units for one condenser. They can be different in size as well to accommodate the area that they serve. The nice thing is that the new inside units can fit in the ceiling, hang on the wall, or even come up from the floor on a raised house. I could do my 1300 sq ft house with 5 heads and be able to have 5 zones instead of one temp for the entire house. There are many days I'm cooling areas I'm hardly in for any length of time.

Costa Mesa is a really mild climate. Is your heating also supplied by the old unit? If you choose you can leave in place for heat as it might run cheaper than all electric.