it would be possible, ive seen a vn with a vs engine, it does mean that u have to exchange the firewall, tho it might be cheaper unless you get all ur infomation correct and have the tools to help. tho i have heard it is possible.
Have read in other threads that it's possible to run the ecotec motor with the earlier ECU which maybe better for performance cause the earlier setup used an MAP sensor and not the MAF sensor like the ecotec. bit of stuffing around however as you would need to adapt the earlier wiring loom to the ecotec and apparently you will need to fit the sensors from the early ECU/engine to the ecotec as well. anthings possible i guess for a price:whistling
just keep your vr ecu and ditch the maf, all you will need to change over is the knock sensor from the vr block and replace one of the knock sensors on the vs block with it. Next up you will need to use one oxygen sensor instead of 2 so you might need to get an exhaust shop to tap a hole in for you after the cat.
Good luck with it all. Also if you stick with the VR ECU it will make getting it tuned later on easier. Plenty of people have been ditching the MAF and using a VR ECU to gain power.