https://github.com/rusefi/rusefi/wiki/Hellen-128-Mercedes is the easiest option if your vehicle has matching harness (ME 2.0/2.1)

https://github.com/rusefi/rusefi/wiki/microRusEFI-Manual smaller universal ECU should be enough for 4 cylinder applications, harness modification required.

https://github.com/rusefi/rusefi/wiki/Proteus-Manual has enough outputs to handle even simpler 12 cylinder engines, harness modification required.