The ipc value does not control production any more, only where you can place them. IC can no longer be placed on islands.
A minor IC puts out 3 units, and can only be built on a territory w/2 ipc or more, cost 12 ipc. It can be SBR for 2x its production (6 damage markers), but comes with its own built in AA gun.
A major IC puts out 10 units, and can only be built on a territory w/3 ipc or more, cost 30 ipc. It can be SBR for 2x its production (20 damage markers), but comes with its own built in AA gun.
You can upgrade a minor IC for 20 ipc (would then be a major), but it would have to be on a territory w/ipc value of at least 3 ipc to start.
Naval bases and air bases can be built on any territory or island, ipc value doesn’t mater (could have no ipc value). Obviously a NB needs a coast line or be on an island. Both AB & NB can be SBR to six damage markers max. If it has 3 damage markers it is inoperable, neither give +1 bonus for movement, AB can’t scramble air units, and NB can’t repair ships. AB & NB also come with built in AA guns.
Hope this helps.