the 305 would take up the same amount of engine space as a 305 so it would have the same amount area to cool,be cool and griffen both make aluminum radiators for the swap so cooling is not really a issue, i wouldn't waste my time with anything smaller then a 350. also i would not go with a 4l60e, for one they are electronic so you would have to have it converted to one wire for a carb set up and also have it beefed up to handle more then four hundred horsepower,go witha th350 or th400 thier dime a dozen and can be beefed up rather cheap