You'll need to get a fob matched to your ECU, I know
http://www.talonsportscars.com/100r.php can do this, I'm sure there are other places.
You may be able to bolt the VVC engine to your 120 box but you'll find it undergeared, I know there are differences between the 2 boxes, I'm not sure what they are though.
www.rovertech.net has a welth of info on the PG1 box.