Should you change your Chevy 305 two bolt main with a Chevy 350 four bolt main or just work on your 305?

you need a 350 put the 305 in the junk yard How long has the 305 lasted? Is it strong enough for you? If you need/want more power, go for a 350. If it's going to get extreme service (racing, heavy hauling), you might need the 4 bolt main, but probably not if it's just normal driving.