From our experience the old style 555 injectors are still vunerable to ethanol related failure. We've had customers who have been switching out their old style injectors for new style in recent months because of failure rate.
I would suggest going Nismo new style 555 (615cc) injectors with 300 Degree rails. That seems to be our most popular fuel system upgrade right now.
Z1 Motorsports 770-838-7777 ex 302 www.300zx.com AIM bryanatZ1