2C in 2.0D is not EFi and is certainly not a "Computer-controlled" engine. You lift the bonnet and there isn't a single electronic sensor to be found. Cruise Control System needs some kind of electronic mapping on engine and information from various sensors in the engine. Since there is no electronic intervention available in the engine hence i think it isn't possible to give Cruise control. I hope I did put it in right words above.
2C is not efi, that is correct, however EFI is not a requirement for cruise control.
The cruise control computer is not dependant on the car's ECU, not unless you're talking about the newer cruise control systems which integrate directly with drive-by-wire (electronic throttle).
Cruise controls were seen in cars as early as 1958, here's a snippet from Wikipedia:
Modern cruise control (also known as a speedostat) was invented in 1945 by the blind inventor and mechanical engineer Ralph Teetor. His idea was born out of the frustration of riding in a car driven by his lawyer, who kept speeding up and slowing down as he talked. The first car with Teetor's system was the Chrysler Imperial in 1958. This system calculated ground speed based on driveshaft rotations and used a solenoid to vary throttle position as needed.
The mechanical throttle cable (like the one in 2.0D and all other non-DBW cars) can be linked to the solenoid and it would be the cruise control computers job to engage and disengage it. Thats how it works on non-DBW cars, so the cars ECU really has nothing to do with it.
There are also vacuum operated cruise controllers, the latest however are the ones which plug directly into DBW cars.
As far as I know, Toyota gets its cruise control systems from Rostra (www.rostra.com), I think they make a cruise control which could fit 2.0D, not sure will need to check.