Ive worked on G54B's a time or two, so heres my take:
Why not run the cam angle sensor off your cam??? The DSM CAS just needs to rotate in phase with the cam, and spin at 1/2 the crank RPM. Use a 2.6L caravan camshaft which extends through the end of the valvecover (originally drove the trans-mounted water pump on the caravan) Those vans are all over in the junkyards...I think they wouldve been made in about 1983-85 era. The vans actually had the cool "Mitsu" valvecovers too, so if you find one, grab that too.
Perhaps you could use something like a lovejoy joint or grind a slot in the caravan cam to couple the two together. Make a custom bracket to mount the CAS, and figure out what orientation it needs to be in to make the engine start.
Is that low-buck enough for you????
The whole basis of EFI swapping is making the computer 'think' the engine is stock.