Amazing project! How you guys make any profit of sort of this is crazy. The asking price must be very high.
IMHO, a stock refreshed rb25 would be great. A built rb in a Z is pointless unless its running some seriously wide, sticky rubber... whoever buys this car will be buying it for the all around performance. I see you have upgraded the brakes and suspension.. very nice.
I recommend a stock rb25 with the basic upgrades (arp, good clutch, etc) it will be running at 400hp+ all day long.
I have a stock rb26 running 450+ and plan to push it further. Nissans are very stout and a built motor will take away from the oem drivability and comfort. try to run this beast on stock cams so the customer will experience a nice idle and good off boost response. gt3076r comes to mind for a turbo.
please post pics when done... its an amazing start to a beautiful car.