the only real difficulty in replacing the ATL series is the automation, which you have said you are happy to live without. Broken down into it's component parts a CPP (which is what any ATL without automation effectively is) consists of:
1. a pump to circulate the water
2. a heater coil and thermostat circuit to control the temperature.
3. a motor to turn the drum with a speed control
4. the gearing from the motor to the drum and the reversing control.
5. the lift

1. should be an off the shelf part
2. should also be an off the shelf solution
3. is allegedly a wiper motor from a BMW. The speed control should be dead simple since the only thing that matters is the output RPM of the motor. Simply calculate the RPM at each of the speeds and then all the replacement has to do is replicate the speeds, not replicate how Jobo does it.
4. should be able to be reused
5. should be able to be reused, or reengineered in metal for more strength.

Broken down into those components you should be able to find a light engineering works that could replicate it relatively easily.

Going further than that involves being able to deliver a precise amount of chemicals from the tanks to the drums so that you can use bulk chemicals rather than measuring them out for each run. There are various solutions to that, but it would be to simpler to avoid altogether and use the CPP/CPA style square bottles (Ilford bottles are the same size) and have enough of them that you can set up three or four runs in advance.