tried to finish tearing down my motor for the cam and head swap.one of my lifters has a big flat spot on it .should i just try and replace the one or buy a hole new set

 

Any time you replace the camshaft, you should replace the lifters, some people say you can reuse the roller style lifters (which I am assuming you have).
I however do not agree, see what ever deformations or imperfections have have been made on the roller of your lifters will be transferred over to the new camshaft. The reason this happens is because the rollers are made from hardened steel, if it has a groove or a flat spot it will make an impression on your cam.