TDI's only started being sold in North America since '98, so they are not that old. Everything before that was IDI, except the bastard child AAZ engine from '93-'97, that was direct injection but pure mechanical pump. Computer controls also start in '98, before that was mechanical pump. '98-'03 still had a rotary distributor style pump, but was computer controlled, '04-'06 started the PD or "pump injector" engine, injectors operated by a cam lobe, but computer controlled. '09 has common rail. VW also does not have urea injection in the exhaust. That's a Mercedes and BMW thing.
VW uses sophisticated catalysts and re-gen cycles to comply to emissions. In the '09s you need to use ULSD or the catalyst will die. Except you can't get anything but ULSD at the pumps anymore.
With that said, making a 4 cyl run on 1 cylinder will make it die a quick death. Run all 4, or get a single cylinder engine.