Is it ok to run the 1 3/4 headers on my 305? I am eventually going to swap in a 350 but it is going to be a little bit before that. Will I lose power? I plan on getting the ceramic coated ones but are they worth it or should I get the regular ones?

 

The headers will be fine with the 305. Having any size headers is better than stock exhaust manifolds so you probably won't notice anything different except a more powerful pull .
SLP headers don't need the coating but I've noticed that the newer 4-1 styles get brown with lots of surface rust rather quick. Mine looks great but it might be because it is a different grade of stainless, not sure. It's up to you with the coating, I wouldn't do it unless you're investing $$$$$$ into a paint job and REALLY care what your exhaust looks like. The surface rust wipes right off with a little elbow grease so don't dump lots of money into a coating if it's a daily driver...that's my opinion.