Good little receivers alright. AOR managed to pack quite a lot of receiver into that case.
Anyway, to the problem at hand: the AR3000 / 3000a needs only a regulated 12 volt input. So long as you get a power supply with the unique AOR power plug on it, cut off the cord, and splice in your own fuse and connect to your own regulated 12 or 13.8 volt power supply. Linear regulated supply would be preferable to a modern switchmode regulated supply, which would cause noise on shortwave frequencies.