what you have, is a lot of nice sized but relatively weak magnets.
you can imitate what the quys do with neo's but you will be disappointed
so to make the best use of them you need to use them all.
with 12" rotors you can only use half of them.
you would need to get another set of rotors and build two mills.
you could grind them flat,(use a diamond blade tile saw)
and place twenty four mags each on two 19.28 dia. disks.
the rotors wont need to be solid steel .
as long as the mags are sitting on a 1/8" strip it should give you enough for a flux return path.
then do a test coil with your wire.
with a curved magnet you may want to consider doing a radial alternator design.
a 48 pole single rotor or a 24pole dual rotor
all i'm suggesting is to make up for the lack of flux density by increasing the frequency.