Sorry coilover I have got to dissagree if the cooling system isn't up to cooling a mild 350 it isn't going to cool a 305. The differance between the two is the bore. I would go with the 350. Sounds to me like you are looking at a rebuild either way. Don't get me wrong the 305 is a good torquie little motor better than the shorter stroke 307. Building any of the SB Chevys in a like mannor will cost about the same. IMO and many others for that mater there is no replacement for displacement.
