Stay away from 1 1/2" primaries. Stay away from anything made by Flowtech or Edelbrock. If you're going to do headers where emissions isn't a major concern, go with full length 1 3/4" primaries and a 3" collector. Any header you can bolt onto a 305 will work on a 350, but many cheap 305 headers will hurt the performance of a larger, healthier engine.

 

Do a search for Dan Burke. His name here is ws6transam search that. He did mods to his 305 H.O. that had it running 14.0 @ 100+