Good advice from Roger. A basic crate engine can often be more cost effective than trying to build or rebuild the engine yourself. Check prices both ways. However, if you've never been into building engines, there is a lot to learn; it may be wise for you to find a friend or family member who has done it before and is willing to "walk you through it" the first time.

One thing that is helpful - small-block Chevy engines are all dimensionally the same on the outside. All the pulleys, brackets, and accessories from your 305 should bolt right on to a 350. Water pump, fuel pump, distributor, alternator and A/C brackets should be a direct interchange.