going to change my cam to a comp cams xr264hr-12.what else will I have to do to the motor?my exhaust will be 3" from cat back to a magnaflow muffler.what kinda chip will I need?will I need to change my injectors?the stock runners ok for now?any thing else I need to do?

 

You will need a custom chip. A mail order one, or something like a hypertech or super chips is not going to do you any good. You will only waste your money. You will need to find somebody that can tune your car under real world driving conditions.
Biggest thing like I had said before is going to be the machine work that you are going to need to do to the heads so that they can accept that cam. You may need to go with screw in studs or the cheaper approach is to pin the studs you have so that they don't pull out with the .495" lift that the cam has.
The other thing is, a cam that is adequate for a 350 will act like a bigger cam on the 305.
The xr264hr12 is a good cam, but don't cut any corners or you will pay for it twice.