Instruments wiring probably won't need to be touched. You probably just need to hook up the alternator so they get the proper power.
I know that McKinney Motorsports makes motor and transmission mounts for the swap.
http://mckinneymotorsports.com/prod_350+Chevy+240sx
You may need a custom driveshaft though.
You can talk to a driveshaft place like Driveshaft Shop, and send them measurements and what transmission + differential you'll be using and they can make you a custom set.
Btw, we have a Hybrid section (Not the Prius kind

) for unique engine swaps.
hybrids.html