You didn't mention if you have fuel injection or a carb. when i replaced my 79 350 w/ a 383 i but a new edelbrock quadrajet that was EGR reay. I replaced my egr too. It was such an easy changeover, i was amazed. see:
www.delbridge.net/installEverything from you 305; alt, a/c, power steering, etc. should bolt right up. Your starter may have to be replaced if it has the two bolts that are not off-set, but paralell to the end of the block. I forget what the 305 starter is but i think it is not off-set bolt pattern. I didnt have to change mine due to it already have the 350 off set bolt pattern.
Email me if you have any questions, been there, done that.
Andy Delbridge
andy@delbridge.net