gonna be awfully hard to make mid 300's with just an intake and injector swap unless you have a power adder. you probably don't even need to change injectors yet. consider buying the intake and sitting on it until you buy heads cam and doing it all at once. you'll be much happier and work less.

just an fyi,
stock 5.0 with stock cam and intake swap might even feel slower down low on the street imo.