problem is the SOHC is lower compression than the DOHC. If you do put the DOHC head on I would reccomend swapping the pistons out for some Miata ones or something.
your right, swapping motors is probably easier than a head swap b/c you would also need to piston swap or face an uber low CR.
Whole motor in and out vs. head pistons and all the other stuff you *should* replace while you have the bottom end apart.