I've thought long and hard a few times about doing this conversion in a Mk 1 Granada using the latest Tranny engine. I'm pretty sure it could be done without too much butchery. At the end of the day it's Ford into Ford, and they've always been very good at inter-changeability. Engine loom can't be that hard to wire up surely? Few sensors required and feeds back to ECU etc? Wldn't think a Sierra would be that different. Have you actually measured the height/width/depth of this engine to see if it will fit in there?