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