I know some people are apprehensive about using a SB400 block because of heating problems. I want to add one more item of personal experience. My wife drove her 70 conv with factory air back from the Tulsa Regionals (remember how hot it was that weekend)with only the original single core radiator which came in the car when it had a 307. I have always intended to have the radiator re-cored with a 3 or 4 core, but just haven't done it yet. The 400 did not show any indication of over heating whatsoever. The ac was cold, the car ran great about 65-70 (I was following with the 56 Vette on a trailer, so that was as fast as I wanted to go) and after we got home and the radiator cooled down, I pulled the cap and the coolant was full. I have added an over flow bottle which I mounted in the space in the fender to the right of the battery. Again, I like all the cubic inches I can get, but sometimes there are reasons a BB is not the way to go. So if you want all the cubes you can get and need to stay with a SB, don't be afraid of a SB400. When you build it, be sure the machine shop vats and cleans the block/heads good, use a good water pump and make sure the radiator is in good shape. If unsure, take the radiator to a shop to be rodded out or have it re-cored. And add an over flow bottle.